Fix handling initial INVITE requests without SDP

Ignore-this: b30fdb7adb69b9ce37d1e64ef6456eb9

darcs-hash:20140902121940-56b4d-1ca6ef3de1a5e3d9e79ab93d31ee1c821add28d8
Fix not ending streams in some cases when Session.remove_streams fails

Ignore-this: 829700468be1b63f0954e2b27f525105

darcs-hash:20140904130936-56b4d-e5c729472ce4842b4696f0b76b6c16bb0457bdda
Fix notification name

Ignore-this: 8e0845a8c403b5f7c064b78507fcfab8

darcs-hash:20140904133744-56b4d-1ebefcc545de4c61459fc80ffa8fb0812d26760f