Add failing test reproducing issue #1015.

There is a race condition when connect and bind on a new inproc
endpoint happen "simultaneously" in threads.  Causes the error:
  Assertion failed: ok (ctx.cpp:474)
Mark failing test for issue #1015 as XFAIL
Merge remote-tracking branch 'upstr/master' into identity_fd
test case for zmq_getsockopt/ZMQ_IDENTITY_FD
Merge branch 'master' of https://github.com/zeromq/libzmq into identity_fd
Merge pull request #1031 from sdrsdr/identity_fd

test case for zmq_getsockopt/ZMQ_IDENTITY_FD
PLAIN: Implement ERROR handling in client
Merge pull request #1032 from hurtonm/master

PLAIN: Implement ERROR handling in client
PLAIN: Fix parsing of ERROR command
PLAIN: Implement ERROR handling in server
Remove debugging output
Merge pull request #1033 from hurtonm/master

Finish ERROR handling for PLAIN mechanism
NULL: Correct ERROR command format
Merge pull request #1034 from hurtonm/master

NULL: Correct ERROR command format
Prefix error-reason with length in ERROR command
Merge pull request #1035 from hurtonm/master

Prefix error-reason with length in ERROR command
CURVE: Implement client-side ERROR handling
Merge pull request #1036 from hurtonm/master

CURVE: Implement client-side ERROR handling
CURVE: Implement server-side ERROR handling
Merge pull request #1038 from hurtonm/master

CURVE: Implement server-side ERROR handling