pgsql: Update constraint_exclusion items: < inheritance, and allow it

Log Message:
-----------
Update constraint_exclusion items:

< inheritance, and allow it to work for UPDATE and DELETE queries

inheritance, allow it to work for UPDATE and DELETE queries, and allow
it to be used for all queries with little performance impact

< * Allow constraint_elimination to be automatically performed
<
< This requires additional code to reduce the performance loss caused by
< constraint elimination.

Modified Files:
--------------
pgsql/doc:
TODO (r1.1637 -> r1.1638)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/TODO.diff?r1=1.1637&amp;r2=1.1638)
pgsql/doc/src/FAQ:
TODO.html (r1.144 -> r1.145)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/FAQ/TODO.html.diff?r1=1.144&amp;r2=1.145)