pgsql: Generic implementation of red-black binary tree.

Log Message:
-----------
Generic implementation of red-black binary tree. It's planned to use in
several places, but for now only GIN uses it during index creation.
Using self-balanced tree greatly speeds up index creation in corner cases
with preordered data.

Modified Files:
--------------
pgsql/src/backend/access/gin:
ginbulk.c (r1.17 -> r1.18)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/gin/ginbulk.c?r1=1.17&r2=1.18)
ginfast.c (r1.6 -> r1.7)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/gin/ginfast.c?r1=1.6&r2=1.7)
gininsert.c (r1.25 -> r1.26)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/gin/gininsert.c?r1=1.25&r2=1.26)
pgsql/src/backend/utils/misc:
Makefile (r1.29 -> r1.30)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/Makefile?r1=1.29&r2=1.30)
pgsql/src/include/access:
gin.h (r1.36 -> r1.37)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/access/gin.h?r1=1.36&r2=1.37)

Added Files:
-----------
pgsql/src/backend/utils/misc:
rbtree.c (r1.1)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/rbtree.c?rev=1.1&content-type=text/x-cvsweb-markup)
pgsql/src/include/utils:
rbtree.h (r1.1)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/rbtree.h?rev=1.1&content-type=text/x-cvsweb-markup)