Use requestSequenceId in sendTApplicationException

The incoming message's seqid is used but this sqid isn't implemented in the same way across languages. The task timeout test in TestPlainServer succeeds because java client maintains an incremental seqid starting from 1. The php client starts from a seqid of 0 and breaks.
Free incoming requests ASAP

Before this change, an expiration timer would hold a reference to a
request until the timer expires (5 seconds by default), even if a reply
gets generated much sooner. The result is that all requests recieved in
the last 5 seconds are held in memory even if most/all could be purged.

This change cancels the expiration timer and allows the GC to free a
request for which a reply has been generated.
Add context data to RequestContext

Summary: This will be used for FBTrace support.
Merge branch 'master' of https://github.com/haijunz/nifty into request_context

Conflicts:
	nifty-core/src/main/java/com/facebook/nifty/core/NiftyDispatcher.java