pgsql: Fix an oversight I introduced on 2003-12-28: find_nots/push_nots - Mailing list pgsql-committers

Log Message:
-----------
Fix an oversight I introduced on 2003-12-28: find_nots/push_nots should
continue to recurse after eliminating a NOT-below-a-NOT, since the
contained subexpression will now be part of the top-level AND/OR structure
and so deserves to be simplified.  The real-world impact of this is
probably minimal, since it'd require at least three levels of NOT to make
a difference, but it's still a bug.
Also remove some redundant tests for NULL subexpressions.

Modified Files:
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    pgsql/src/backend/optimizer/prep:
        prepqual.c (r1.49 -> r1.50)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/prep/prepqual.c.diff?r1=1.49&r2=1.50)