repair deep-copying (and pickling) of the control flow state in compiled Cython (extension type instances lost their state)

Fix a memory leak in ObjectHandling.c

do not use cythonize() but Cython.Distutils in setup.py to avoid Cython compilation when not building the extensions

clean up extension building in setup.py: clarify what's Py3.2-specific and use cythonize() instead of Cython.Distutils

* Add Python 3.5 to the build matrix
* Rework helper build script (copied from mpi4py)

guess longness suffix of negative decimal integer literals based on their type to prevent the C compiler from truncating their value range

Though this path is never taken for unsigned ints, MSVC still throws
warning C4146.