Factor out window bits value validation code into a separate function.

Release note: n/a
Review URL: https://codereview.appspot.com/7643044

git-svn-id: http://pywebsocket.googlecode.com/svn/trunk@739 4ff78f4a-9131-11de-b045-6380ec9940d4
Move out the code for the deflate-stream extension into a separate file.

Release note: DeflateStreamExtensionProcessor moves to deflate_stream_extension.py.
Review URL: https://codereview.appspot.com/7847043

git-svn-id: http://pywebsocket.googlecode.com/svn/trunk@740 4ff78f4a-9131-11de-b045-6380ec9940d4