Revert r42943: Revert #6750 and related tickets

Please see http://twistedmatrix.com/pipermail/twisted-python/2014-November/028912.html for more details.

Reopens: #6970


git-svn-id: svn://svn.twistedmatrix.com/svn/Twisted/trunk@43430 bbbe8e31-12d6-0310-92fd-ac37d47ddeeb