Move _helper.c's Python.h back up (now to the top), because Python.

Move the Python.h include in _helper.c to the top because Python says
so:

  http://docs.python.org/2/c-api/intro.html#include-files

Though according to this, it's been fixed upstream:

  http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=206805

Which might explain why I didn't see the problem here.

Thanks to Chandan Kumar <chandank.kumar@gmail.com> for the report.

Signed-off-by: Rob Browning <rlb@defaultvalue.org>