pgsql: Separate predicate-testing code out of indxpath.c, making it a

Log Message:
-----------
Separate predicate-testing code out of indxpath.c, making it a module
in its own right. As proposed by Simon Riggs, but with some editorializing
of my own.

Modified Files:
--------------
pgsql/src/backend/optimizer/path:
indxpath.c (r1.182 -> r1.183)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/path/indxpath.c.diff?r1=1.182&r2=1.183)
pgsql/src/backend/optimizer/plan:
createplan.c (r1.191 -> r1.192)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/plan/createplan.c.diff?r1=1.191&r2=1.192)
pgsql/src/backend/optimizer/util:
Makefile (r1.15 -> r1.16)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/util/Makefile.diff?r1=1.15&r2=1.16)
pgsql/src/backend/utils/adt:
selfuncs.c (r1.180 -> r1.181)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/selfuncs.c.diff?r1=1.180&r2=1.181)
pgsql/src/include/optimizer:
paths.h (r1.84 -> r1.85)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/optimizer/paths.h.diff?r1=1.84&r2=1.85)

Added Files:
-----------
pgsql/src/backend/optimizer/util:
predtest.c (r1.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/util/predtest.c?rev=1.1&content-type=text/x-cvsweb-markup)
pgsql/src/include/optimizer:
predtest.h (r1.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/optimizer/predtest.h?rev=1.1&content-type=text/x-cvsweb-markup)