Change media data attribute of SCSessionNewIncoming to list of strings

darcs-hash:20090319200732-58103-1d7498e31b7aac9e23e5f781f205598689badfa4
Change media data attribute of SCSessionGotStreamProposal to list of strings

darcs-hash:20090319201715-58103-29b12d54af4bb1126d21cd8ba3f3d2a6bdefabd9