Python 3 support

I wrote some python 3 support. And tested it manually with python 3.2 and python 2.7. 

.encode() - to store bytes() (str() equivalent in python 3)

>>> import pylibmc
>>> mc = pylibmc.Client(["10.0.0.1"])
>>> mc["test".encode('utf-8')] = "Some value".encode('utf-8')
>>> mc["test".encode('utf-8')]
b'Some value'


Please have a look at it.