pgsql: Update based on user comments: < in PL/PgSQL is to use

Log Message:
-----------
Update based on user comments:

< in PL/PgSQL is to use EXECUTE.

in PL/PgSQL is to use EXECUTE. One complexity is that a function
might itself drop and recreate dependent tables, causing it to
invalidate its own query plan.

Modified Files:
--------------
pgsql/doc:
TODO (r1.1638 -> r1.1639)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/TODO.diff?r1=1.1638&amp;r2=1.1639)
pgsql/doc/src/FAQ:
TODO.html (r1.145 -> r1.146)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/FAQ/TODO.html.diff?r1=1.145&amp;r2=1.146)