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/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>