add compat functions for the deprecated PyCObject api

* Moved to using the PyCapsule API for python >= 3
* PyCObject is removed from Python 3.2
* It has also been deprecated in 2.7 but since we use the API in header files
  which are consumed by static binding modules, appling this for python 2.7
  causes crashes unless the modules are recompiled, breaking ABI.  It is safe
  to rely on for 2.7 because it will never be removed and there is talk of
  undeprecating it upstream.
* There is no issues with static bindings under python 3 because they are not
  supported yet and most likely never will be.
* Even if PyCObject is brought back in 3.2, PyCapsule is a much safer API
  which adds a poorman's type check when unboxing.

https://bugzilla.gnome.org/show_bug.cgi?id=630844