pgsql: Suppress subquery pullup/pushdown when a subquery contains

Log Message:
-----------
Suppress subquery pullup/pushdown when a subquery contains volatile
functions in its targetlist, to avoid introducing multiple evaluations
of volatile functions that textually appear only once.  This is a
slightly tighter version of Jaime Casanova's recent patch.

Modified Files:
--------------
    pgsql/src/backend/optimizer/path:
        allpaths.c (r1.151 -> r1.152)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/path/allpaths.c.diff?r1=1.151&r2=1.152)
    pgsql/src/backend/optimizer/prep:
        prepjointree.c (r1.42 -> r1.43)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/prep/prepjointree.c.diff?r1=1.42&r2=1.43)