Fourth version of the patch attached. It is rebased to the HEAD (8879fa0).
Operator name formatting patch rebased on top of it. I will put
the selectivity estimation patch to the next commit fest.
This version of the patch does not touch to the btree_gist extension,
does not set the operator class as the default. It adds support to
the not equals operator to make the operator class compatible with
the btree_gist extension.
