Fixed session2's handling of unknown media types

Ignore-this: 4c4e43d542f6ecd67b3a4568b58742b7

darcs-hash:20090520065010-1e3d8-4cff18381e3e54e4dd3e2857c50ac287b3d0c65c
Update TODO

darcs-hash:20090521073703-58252-fcd4d2a875dfccfcf7f416c2d24ce6bff7a0c7f4