Add point_ops opclass for GiST.

src/backend/access/gist/gistproc.c

src/backend/utils/adt/geo_ops.c

src/include/catalog/catversion.h

src/include/catalog/pg_amop.h

src/include/catalog/pg_amproc.h

src/include/catalog/pg_opclass.h

src/include/catalog/pg_operator.h

src/include/catalog/pg_opfamily.h

src/include/catalog/pg_proc.h

src/include/utils/geo_decls.h

src/test/regress/expected/create_index.out

src/test/regress/expected/opr_sanity.out

src/test/regress/expected/point.out

src/test/regress/expected/sanity_check.out

src/test/regress/sql/create_index.sql

src/test/regress/sql/point.sql