Fixes #288 #287 #277

Multiple fixes for milestone 0.4.1

#277 Short-circuiting if `PassThruObserver` is already draining the notifications. Since, the observer is serialized, this only ensures that we do not drain recursively on every re-entrant call.
#287 Flushing `HttpServerResponse` when the `Observable` returned from `RequestHandler.handle()` terminates. Added a method `flushOnlyOnChannelReadComplete()` to turn off this auto-flush on terminate.
#288 Upgraded to rxjava-1.0.1