* Add lb_t::sendpipe() that returns the pipe that was used for sending,
similar to fq_t::recvpipe().
* Add forwarder functions to dealer_t to access these two.
* Add logic to req_t to ignore replies on pipes that are not the one
where the request was sent.
* Enable test in test_spec_req.
* disabled the specific tests that do not work (yet) on libzmq
* cleaned up one source (test_spec_rep.c) but the others need similar work
* added sleep in test_spec_rep to allow connects time to happen; this would
not be needed if we connected out to the REP peers instead in from them,
but I didn't want to change the logic of the test code.
* See http://rfc.zeromq.org/spec:28/REQREP
* Not all testable statements are covered.
* At this point, there are several failures:
- test_spec_req: The REQ socket does not correctly discard messages
from peers that are not currently being talked to.
- test_spec_dealer/router: On disconnect, the queues seem to not be
emptied. The DEALER can still receive a message the disconnected
peer sent, the ROUTER can still send to the identity of the dis-
connected peer.
