Some systems (e.g. Arch Linux) put the Python C headers in a strange
place, so try and run `$PYTHON-config --includes` first to find the -I
options to pass to the C compiler. Fall back to the old method if it
fails.
Thanks to Darrell Enns for reporting the problem and suggesting a
solution. I changed it a bit.
Here's a small patch to make the configure script compatible with Python
3. The wrapper itself (swig/python/comedi_python_wrap.c) will have to be
generated with SWIG >= 2.0.0 for Python 3 compatibility.
