[Zope] Important Fix for Zope 2.0 through 2.1.6

Thanks to Jeff Ragsdale, we've finally been able to kill a longstanding bug that allows POST requests to interfere with each other. Symptoms include corrupted or aborted File and Image uploads, and stupid-log messages about "AttributeError: data" killing threads. The attached HTTPServer.py is valid for all Zope 2.0.x and 2.1.x versions. I am posting the patched file for Zope 2.2.x separately. PLEASE BACK UP <Zope>/ZServer/HTTPServer.py, then replace it with the attached file. Cheers, Evan @ digicool & 4-am