libffi.h in the wrong place
Revert reverting the libffi patch, adding the includedir to python environment instead

This reverts commit fc3b457a56d0a814a3d010d8738ed952f17922a9.
Finished release v2.7.6.12.

* release/v2.7.6.12:
  Revert reverting the libffi patch, adding the includedir to python environment instead
  libffi.h in the wrong place