[Distutils] Optional C extensions and setuptools

[Bob Ippolito]

I've just added a small optional C extension to simplejson to speed up
decoding, but I have a feeling that it's going to cause problems for
Windows users.

Right now it's specified as setuptools Feature the same way that
PyProtocols' speedups module is implemented.

Is there something I can do in the setup.py to fail gracefully and
install anyways if it can't compile the extension? In some way that's
compatible with easy_install?

-bob