pgsql: Remove contrib version of rtree_gist --- now in core system.

Log Message:
-----------
Remove contrib version of rtree_gist --- now in core system.

Modified Files:
--------------
pgsql/contrib:
Makefile (r1.56 -> r1.57)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/Makefile.diff?r1=1.56&r2=1.57)
README (r1.78 -> r1.79)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/README.diff?r1=1.78&r2=1.79)

Removed Files:
-------------
pgsql/contrib/rtree_gist:
Makefile
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/rtree_gist/Makefile)
README.rtree_gist
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/rtree_gist/README.rtree_gist)
rtree_gist.c
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/rtree_gist/rtree_gist.c)
rtree_gist.sql.in
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/rtree_gist/rtree_gist.sql.in)
pgsql/contrib/rtree_gist/bench:
bench.pl
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/rtree_gist/bench/bench.pl)
create_test.pl
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/rtree_gist/bench/create_test.pl)
pgsql/contrib/rtree_gist/data:
test_box.data
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/rtree_gist/data/test_box.data)
pgsql/contrib/rtree_gist/expected:
rtree_gist.out
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/rtree_gist/expected/rtree_gist.out)
pgsql/contrib/rtree_gist/sql:
rtree_gist.sql
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/rtree_gist/sql/rtree_gist.sql)