Do not add observer for no longer used notifications

Ignore-this: efc5ad20fa015ea893f0b97e83089c69

darcs-hash:20140113121157-b22ec-115b5f938a928e07f43337abaed09fc5e1291790
Initialize transport to None in MSRPStreamBase.__init__

Ignore-this: 420fcca8292cd674ce39f56d1b81616b

darcs-hash:20140130124853-b22ec-ee8c973953229597dae3b895412575dffc9eb86d
Accept unicode in SIPURI objects

Ignore-this: 1aee5f5662db0ed3204e26bcef7409c0

darcs-hash:20140204131122-56b4d-74e4e29d46169d6d2975f4e1260269eddc23f600