doc: add commas after 'i.e.' and 'e.g.'

This follows the American format,
https://jakubmarian.com/comma-after-i-e-and-e-g/. There is no intention
of requiring this format for future text, but making existing text
consistent every few years makes sense.

Discussion: https://postgr.es/m/20200825183619.GA22369@momjian.us

Backpatch-through: 9.5

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

@@ -586,7 +586,7 @@ EOF
 
   <para>
    <application>psql</application> returns 0 to the shell if it
-   finished normally, 1 if a fatal error of its own occurs (e.g. out of memory,
+   finished normally, 1 if a fatal error of its own occurs (e.g., out of memory,
    file not found), 2 if the connection to the server went bad
    and the session was not interactive, and 3 if an error occurred in a
    script and the variable <varname>ON_ERROR_STOP</varname> was set.
@@ -2344,7 +2344,7 @@ lo_import 152801
           In <literal>latex-longtable</literal> format, this controls
           the proportional width of each column containing a left-aligned
           data type.  It is specified as a whitespace-separated list of values,
-          e.g. <literal>'0.2 0.2 0.6'</>.  Unspecified output columns
+          e.g., <literal>'0.2 0.2 0.6'</>.  Unspecified output columns
           use the last specified value.
           </para>
           </listitem>
@@ -3532,7 +3532,7 @@ testdb=&gt; \set PROMPT1 '%[%033[1;33;40m%]%n@%/%R%[%033[0m%]%# '
     <application>psql</application> starts up. Tab-completion is also
     supported, although the completion logic makes no claim to be an
     <acronym>SQL</acronym> parser.  The queries generated by tab-completion
-    can also interfere with other SQL commands, e.g. <literal>SET
+    can also interfere with other SQL commands, e.g., <literal>SET
     TRANSACTION ISOLATION LEVEL</>.
     If for some reason you do not like the tab completion, you
     can turn it off by putting this in a file named