<rdar://problem/4763519> REGRESSION: Multipart/x-mixed-replace sub-resources fail to load

        * Loader/WebSubresourceLoader.m:
        (+[WebSubresourceLoader startLoadingResource:withRequest:customHeaders:referrer:forFrameLoader:]): 
        Enable multipart/x-mixed-replace support on the request.  This line was accidently removed during 
        some loader refactoring.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@16742 268f45cc-cd09-0410-ab3c-d52691b4dbfc