BUG #6401: IS DISTINCT FROM improperly compares geomoetric datatypes

The following bug has been logged on the website:

Bug reference:      6401
Logged by:          Kenaniah Cerny
Email address:      kenaniah@gmail.com
PostgreSQL version: 9.1.2
Operating system:   Centos 6 x86_64
Description:=20=20=20=20=20=20=20=20

----
SELECT point(2, 3) IS DISTINCT FROM point(2, 3);
----
ERROR:  operator does not exist: point =3D point
LINE 1: SELECT point(2, 3) IS DISTINCT FROM point(2, 3)
                           ^
HINT:  No operator matches the given name and argument type(s). You might
need to add explicit type casts.
----

According to the docs
(http://www.postgresql.org/docs/current/static/functions-geometry.html#FUNC=
TIONS-GEOMETRY),
the "same as" operator is the ~=3D operator,  not the =3D operator.=20

This problem cascades to the comparison of complex types, such as "OLD IS
DISTINCT FROM NEW" in the context of plpgsql.=20