Hmm.  In 3.0 and 2.7, I get:

>>> from struct import pack
>>> pack('L', 123.0)
sys:1: DeprecationWarning: integer argument expected, got float
b'{\x00\x00\x00'

So it looks like we already changed py3k to get rid of the 
DeprecationWarning.

I think the idea was that eventually *only* integers would be accepted 
for the integer format codes.  So pack('L', 123.0) should ideally raise 
TypeError.  If we're not going to do that, we should at least put the 
DeprecationWarning back in, but it seems better to actually go ahead 
with the deprecation.