This can be useful if some external objects have to be cleaned up when
the Python object dies. Otherwise the cyclic garbage collector may
drop the references before the cleanup has any chance to run.

Includes documentation and a simple unit test.

Discussion: http://article.gmane.org/gmane.comp.python.cython.devel/14986

Better to crash early than to never know that the reference changed to
None. See discussion here:

http://article.gmane.org/gmane.comp.python.cython.devel/14833

properly handle expressions at the beginning of func/class/etc. blocks that start with a string literal but are not docstrings

always set __path__ for compiled packages and in Py3.3 actually implement finding the file path at module init time by rerunning the import lookup

move getattr() utility code from Builtins.c to ObjectHandling.c as it deals with object protocols and is not a required replacement