Boolean casting in 7.3 -> changed?

A quick question:

in 7.3 the following no longer works:

template1=> select 0::bool;
ERROR: Cannot cast type integer to boolean

The statement must be rewritten as this:

template1=> select '0'::bool;
bool
------
f
(1 row)

Is there a reason for this?
I ask because the former query works in 7.1.3 and 7.2.1,
but I haven't seen any mention of a change in 7.3 (at
least not in the release notes).

Apologies if this has been discussed to death previously,
but it might be worth mentioning somewhere as a "gotcha".

Ian Barwick
barwick(at)gmx(dot)net