[MERGE][0.91?] './setup.py install' on systems without gcc didn't work for me

[Martin Pool]

> > Your patch don't help on Windows, because there build_ext try to
> > find suitable C compiler earlier, in run() method.
> > I update your patch to support win32 as well.
>
> Sorry, forgot to re-raise error on non-win32.
> Updated version attached.

Should we actually be re-raising on other platforms?  Why not give a
warning everywhere if the point is to make it optional?

-- 
Martin