use cython_ifdef.py script - add preprocessor to core_.pyx; add Makefile to run cython-related things.

so they don't get confused with #if preprocessor directive

BACKWARD INCOMPATIBLE: Queue(0) is now the same as Queue(None). This simplifies implementation and removes the difference between
gevent's Queue and queues from Queue and multiprocessing. Use Channel instead of Queue(0).

pywsgi: set max_accept to 1 if environ['wsgi.multiprocess'] is true (e.g. in case of gunicorn having >1 workers)

add DEFAULT_MAX_ACCEPT to server.py: StreamServer.max_accept is now None and set to DEFAULT_MAX_ACCEPT before starting listening