Py3k:  remove Py3 syntax errors.
Get '_proxy.c' compiling under Py3k.
Get '_zope_security_checker.c' compiling under Py3k.
Fix module initialization.
Get all tests passing (or suppressed) on Py3k.
Suppress Py3k nannyisms.
Note Py3k support.

Add Trove classifiers for supported versions.

Note that PyPy is not yet supported:  we need a pure-Python version
of the _proxy and _zope_security_checker implementations.