Problem: f2321644b2 does not work for third level
Problem: f2321644b2 does not work for third level

Solution: generate _cdefs.inc files to be included in cdefs source code

TL;DR;
Situation with libA -> libB -> libC leads to recursive-slurp problem, where all
the definition files are recursively included on top of others. Leading to nonsence
and invalid Python syntax.

This patch creates _cdefs.inc, which is the directly included in cdefs.py during
code generation. That way we can ensure all our definitons are a part of one
ffi instance and all the automagic around code generation works.

zeromq/zproject,paddor/zproject,zeromq/zproject,paddor/zproject,paddor/zproject,zeromq/zproject