[e] (0) cross-reference for multipart/x-mixed-replace
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=22236
Affected topics: Video and Audio

git-svn-id: http://svn.whatwg.org/webapps@7963 340c8d12-0b0e-0410-8428-c7bf67bfef74

 Author:    ianh <ianh@340c8d12-0b0e-0410-8428-c7bf67bfef74>