Fixed ChatStream's local_identity and remote_indentity to be threadsafe

Ignore-this: f6d190ce338b0b0223b6761c2d2b7eab

darcs-hash:20121016132628-b22ec-3d2dd4db00577c85daeda807e2043e58f7693c11
Ignore closed sessions on setting local nickname and avoid threading issues

Ignore-this: 4255e5a04aff4818dbe5cca85f8bf91b

darcs-hash:20121016143122-b22ec-e52d616f6bba4cb96407191079a721c3899eaaa9