Add SphinxBuilder to t.p._release

git-svn-id: svn://svn.twistedmatrix.com/svn/Twisted/branches/sphinx-conversion-4500@32829 bbbe8e31-12d6-0310-92fd-ac37d47ddeeb
Expand test for SphinxBuilder

git-svn-id: svn://svn.twistedmatrix.com/svn/Twisted/branches/sphinx-conversion-4500@32830 bbbe8e31-12d6-0310-92fd-ac37d47ddeeb
Add SphinxBuild test for failing case (when running sphinx-build fails)

git-svn-id: svn://svn.twistedmatrix.com/svn/Twisted/branches/sphinx-conversion-4500@32831 bbbe8e31-12d6-0310-92fd-ac37d47ddeeb