Fix C++ reference to C++ reference coercion

with some improvements to previously committed test case

This commit allows you to pass in variables for the conditional compilation
feature from distutils. This allows you to do fairly complex autoconf-type
checks from setup.py and pass the results in to the compiler.

This is an update to the change in ticket #323 here:
http://trac.cython.org/cython_trac/ticket/323

DefNode refactoring and initial closure function call inlining