application.cgirun() behaves not as expected on GAE

[Alex Koshelev]

application.cgirun() doc string suggests such use case:

"""
Return a CGI handler. This is mostly useful with Google App Engine.
There you can just do:

main = app.cgirun()
"""

But in case of GAE cgirun() always returns None. It executed WSGI application once and returns (GAE's `run_wsgi_app` even daesn't have explicit return statement!).

It cause GAE not to cache handler module as expected.