pgsql: Fix constraint exclusion to work in inherited UPDATE/DELETE

Log Message:
-----------
Fix constraint exclusion to work in inherited UPDATE/DELETE queries
... in fact, it will be applied now in any query whatsoever. I'm still
a bit concerned about the cycles that might be expended in failed proof
attempts, but given that CE is turned off by default, it's the user's
choice whether to expend those cycles or not. (Possibly we should
change the simple bool constraint_exclusion parameter to something
more fine-grained?)

Modified Files:
--------------
pgsql/doc/src/sgml:
config.sgml (r1.45 -> r1.46)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/config.sgml.diff?r1=1.45&r2=1.46)
ddl.sgml (r1.51 -> r1.52)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ddl.sgml.diff?r1=1.51&r2=1.52)
pgsql/src/backend/optimizer/path:
allpaths.c (r1.141 -> r1.142)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/path/allpaths.c.diff?r1=1.141&r2=1.142)
joinpath.c (r1.100 -> r1.101)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/path/joinpath.c.diff?r1=1.100&r2=1.101)
pgsql/src/backend/optimizer/util:
plancat.c (r1.117 -> r1.118)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/util/plancat.c.diff?r1=1.117&r2=1.118)
pgsql/src/include/optimizer:
plancat.h (r1.37 -> r1.38)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/optimizer/plancat.h.diff?r1=1.37&r2=1.38)