Avoid two requests on a TypeError

Rather than test behavior via try: except, inspect python version
number.  

NOTE: This may not be a huge issue in real life. 

I noticed it using wsgi-intercept where an intercepted app raised a
TypeError (which got bubbled up the stack to this catch). If the purpose of this code is as the comments say, checking sys.version_info is probably a more efficient and predictable.  But maybe more is happening here than I've investigated?

anyway, this is a friendly testless PR, feel free to disregard ;)