cleanup the mess when exception occurs
- exception in frame header reader are reported to the client (should no more be stalled)
- exception in frame body reader are reported to the client
- general exception (like connection lost) should be reported to all clients (should no more be stalled)
- dispose takes care to wake up all pending clients with a cancel exception
Adding Pierre C. changes.
Merge remote-tracking branch 'upstream/master'

Conflicts:
	CassandraSharp/Transport/Connection.cs
	Samples/Program.cs