Fixed overwrite in zmq_getsockopt

add exhaustive comparison in testutil bounce

On ZMQ_CURVE_xxxKEY fetches, would return 41 bytes into caller's 40-byte
buffer. Now these fetches only return 41 bytes if the caller explicitly
provides a 41-byte buffer (i.e. the option size is 41).

Fix preprocessor typoe

Minor fixes to project packaging

Fix Makefile.am for test_ctx_destroy

Implement non-blocking shutdown command

Fixed minor error in NULL mechanism (spec was wrong)

* This is passed to the ZAP handler in the 'domain' field

* If not set, or empty, then NULL security does not call the ZAP handler

* This resolves the phantom ZAP request syndrome seen with sockets where
  security was never intended (e.g. in test cases)

* This means if you install a ZAP handler, it will not get any requests
  for new connections until you take some explicit action, which can be
  setting a username/password for PLAIN, a key for CURVE, or the domain
  for NULL.

Fix tests on windows

Updated libzmq to match RFCs 

- was not looping to read all input from peer
- broke on OS/X specifically

Clarified zmq_socket.txt ZMQ_STREAM section, added HTTP server example

- tests that system can provide at least 1,000 sockets
- we could expand on this but this covers the main case of OS/X
  having a too-low default limit of 256 handles per process

mark test_linger as expected failure