[Cython] Class module names do not respect package hierarchy

[Stefan Behnel]

Stephane DROUARD wrote:
> There are maybe some other situations where Pyrex/Cython hardcodes the
> module name in the generated code, but I'm quite confident that they can
> be replaced by the module's name retrieved at runtime.

I'm not sure this is the case for cimports of external extension types
(which are imported at runtime). This will have to be verified before such
a change can be accepted.

Stefan