Improve SQL function disallowed command wording.

doc/src/sgml/xfunc.sgml

@@ -116,7 +116,7 @@
      Besides <command>SELECT</command> queries, the commands can include data
      modification queries (<command>INSERT</command>,
      <command>UPDATE</command>, and <command>DELETE</command>), as well as
-     other SQL commands. (You cannot put transaction commands, e.g.
+     other SQL commands. (You cannot use transaction control commands, e.g.
      <command>COMMIT</>, <command>SAVEPOINT</>, and some utility
      commands, e.g.  <literal>VACUUM</>, into an <acronym>SQL</acronym> function.)
      However, the final command