Use the correct article for abbreviations

We've accumulated quite a mix of instances of "an SQL" and "a SQL" in the
documents.  It would be good to be a bit more consistent with these.

The most recent version of the SQL standard I looked at seems to prefer
"an SQL".  That seems like a good lead to follow, so here we change all
instances of "a SQL" to become "an SQL".  Most instances correctly use
"an SQL" already, so it also makes sense to use the dominant variation in
order to minimise churn.

Additionally, there were some other abbreviations that needed to be
adjusted. FSM, SSPI, SRF and a few others.  Also fix some pronounceable,
abbreviations to use "a" instead of "an".  For example, "a SASL" instead
of "an SASL".

Here I've only adjusted the documents and error messages.  Many others
still exist in source code comments.  Translator hint comments seem to be
the biggest culprit.  It currently does not seem worth the churn to change
these.

Discussion: https://postgr.es/m/CAApHDvpML27UqFXnrYO1MJddsKVMQoiZisPvsAGhKE_tsKXquw%40mail.gmail.com

doc/src/sgml/ref/alter_opfamily.sgml

@@ -269,7 +269,7 @@ ALTER OPERATOR FAMILY <replaceable>name</replaceable> USING <replaceable class="
   </para>
 
   <para>
-   The operators should not be defined by SQL functions.  A SQL function
+   The operators should not be defined by SQL functions.  An SQL function
    is likely to be inlined into the calling query, which will prevent
    the optimizer from recognizing that the query matches an index.
   </para>

doc/src/sgml/ref/create_function.sgml

@@ -701,7 +701,7 @@ CREATE FUNCTION foo(int, int default 42) ...
   <title>Examples</title>
 
   <para>
-   Add two integers using a SQL function:
+   Add two integers using an SQL function:
 <programlisting>
 CREATE FUNCTION add(integer, integer) RETURNS integer
     AS 'select $1 + $2;'

doc/src/sgml/ref/create_opclass.sgml

@@ -265,7 +265,7 @@ CREATE OPERATOR CLASS <replaceable class="parameter">name</replaceable> [ DEFAUL
   </para>
 
   <para>
-   The operators should not be defined by SQL functions.  A SQL function
+   The operators should not be defined by SQL functions.  An SQL function
    is likely to be inlined into the calling query, which will prevent
    the optimizer from recognizing that the query matches an index.
   </para>

doc/src/sgml/ref/create_statistics.sgml

@@ -208,7 +208,7 @@ EXPLAIN ANALYZE SELECT * FROM t1 WHERE (a = 1) AND (b = 0);
 
   <para>
    Create table <structname>t2</structname> with two perfectly correlated columns
-   (containing identical data), and a MCV list on those columns:
+   (containing identical data), and an MCV list on those columns:
 
 <programlisting>
 CREATE TABLE t2 (

doc/src/sgml/ref/create_trigger.sgml

@@ -515,7 +515,7 @@ UPDATE OF <replaceable>column_name1</replaceable> [, <replaceable>column_name2</
    as <literal>ON UPDATE CASCADE</literal> or <literal>ON DELETE SET NULL</literal>, are
    treated as part of the SQL command that caused them (note that such
    actions are never deferred).  Relevant triggers on the affected table will
-   be fired, so that this provides another way in which a SQL command might
+   be fired, so that this provides another way in which an SQL command might
    fire triggers not directly matching its type.  In simple cases, triggers
    that request transition relations will see all changes caused in their
    table by a single original SQL command as a single transition relation.

doc/src/sgml/ref/pg_dump.sgml

@@ -1413,7 +1413,7 @@ CREATE DATABASE foo WITH TEMPLATE template0;
   <title>Examples</title>
 
   <para>
-   To dump a database called <literal>mydb</literal> into a SQL-script file:
+   To dump a database called <literal>mydb</literal> into an SQL-script file:
 <screen>
 <prompt>$</prompt> <userinput>pg_dump mydb &gt; db.sql</userinput>
 </screen>

doc/src/sgml/ref/pgbench.sgml

@@ -1012,7 +1012,7 @@ pgbench <optional> <replaceable>options</replaceable> </optional> <replaceable>d
     Before <productname>PostgreSQL</productname> 9.6, SQL commands in script files
     were terminated by newlines, and so they could not be continued across
     lines.  Now a semicolon is <emphasis>required</emphasis> to separate consecutive
-    SQL commands (though a SQL command does not need one if it is followed
+    SQL commands (though an SQL command does not need one if it is followed
     by a meta command).  If you need to create a script file that works with
     both old and new versions of <application>pgbench</application>, be sure to write
     each SQL command on a single line ending with a semicolon.
@@ -1030,7 +1030,7 @@ pgbench <optional> <replaceable>options</replaceable> </optional> <replaceable>d
    <xref linkend="pgbench-automatic-variables"/>. A value specified for these
    variables using <option>-D</option> takes precedence over the automatic presets.
    Once set, a variable's
-   value can be inserted into a SQL command by writing
+   value can be inserted into an SQL command by writing
    <literal>:</literal><replaceable>variablename</replaceable>.  When running more than
    one client session, each session has its own set of variables.
    <application>pgbench</application> supports up to 255 variable uses in one

doc/src/sgml/ref/psql-ref.sgml

@@ -1044,7 +1044,7 @@ testdb=>
         For <literal>\copy ... from stdin</literal>, data rows are read from the same
         source that issued the command, continuing until <literal>\.</literal>
         is read or the stream reaches <acronym>EOF</acronym>. This option is useful
-        for populating tables in-line within a SQL script file.
+        for populating tables in-line within an SQL script file.
         For <literal>\copy ... to stdout</literal>, output is sent to the same place
         as <application>psql</application> command output, and
         the <literal>COPY <replaceable>count</replaceable></literal> command status is
@@ -2243,7 +2243,7 @@ Tue Oct 26 21:40:57 CEST 1999
         <listitem>
         <para>
          Sends the current query buffer to the server, then treats
-         each column of each row of the query's output (if any) as a SQL
+         each column of each row of the query's output (if any) as an SQL
          statement to be executed.  For example, to create an index on each
          column of <structname>my_table</structname>:
 <programlisting>
@@ -3510,7 +3510,7 @@ testdb=&gt; <userinput>\setenv LESS -imx4F</userinput>
         </para>
 
         <para>
-        Normally, <application>psql</application> will dispatch a SQL command to the
+        Normally, <application>psql</application> will dispatch an SQL command to the
         server as soon as it reaches the command-ending semicolon, even if
         more input remains on the current line.  Thus for example entering
 <programlisting>