Partitioning on ip4 datatype using <<=

I'm trying to partition my table on the first octet of an ip4 column
and can't seem to get the planner to do the constraint_exclusion. The
following SQL (copied by hand):

CREATE TABLE a (ip ip4);
CREATE TABLE a_1 ( CHECK (ip <<= '1.0.0.0/8' ) INHERITS(a);
CREATE TABLE a_2 ( CHECK (ip <<= '2.0.0.0/8' ) INHERITS(a);
CREATE TABLE a_3 ( CHECK (ip <<= '3.0.0.0/8' ) INHERITS(a);
CREATE TABLE a_4 ( CHECK (ip <<= '4.0.0.0/8' ) INHERITS(a);
SET constraint_exclusion = on;
EXPLAIN SELECT * FROM a WHERE ip <<= '1.0.0.0/8'

tells me that its going to do a sequential scan across all of the
tables.

Couple of questions:
-Can you see anything immediate/stupid that I'm doing wrong? I'm
thinking that maybe it has something to do with the constraint types
...

-Does the partitioning understand the '<<=' check? I created a set of
trial tables that used '=' instead on the ip4 column and things behaved
as they should.

-If I have overlapping/duplicate constraints, will constraint_exclusion
scan only the tables that satisfy the constraints, or will it get
confused and bail? I'm thinking of having a 'normal' and an 'old'
partition on the same octet, so the check constraint will be the same
for both of them.

-Will the planner use the constraint exclusion if my queries are of the
form " ip = '1.2.3.4' ", i.e. does the planner understand that '<<='
provides a superset of '='?

Thanks
-Mike