ADD CONSTRAINT behaviour question

When adding unique keys:

* If you do this, you get two unique keys (7.0.3):

create table test (int4 a, int4 b);
create unique index indx1 on test(a, b);
create unique index indx2 on test(a, b);

Then you get this:
         Table "test"Attribute |  Type   | Modifier
-----------+---------+----------a         | integer |b         | integer |
Indices: asdf,        asdf2

* If you do this, you only get two unique keys (7.0.3):

create table test (a int4, b int4, unique(a, b), unique(a, b));

Then you get this:
         Table "test"Attribute |  Type   | Modifier
-----------+---------+----------a         | integer |b         | integer |
Indices: test_a_key,        test_a_key1

* So, does this mean that my ALTER TABLE/ADD CONSTRAINT code should happily
let people define multiple unique indices over the same columns?

* As a corollary, should it prevent people from adding more than one primary
key constraint?

Chris

ps. I know I only tested these on 7.0.3 - but I assume HEAD has similar
behaviour?