Add "comedi_python.i" swig interface file which merely %includes the
"comedi.i" in the parent directory. Fix paths in "setup.py" and set it up
to run swig directly (using "comedi_python.i" as the source). Change
"_comedi.py" to "comedi.py" (but keep the underscore prefix on the .so
and .la files).
Based on a patch by W. Trevor King.
