Ported from libxs revision 123c0f5387ecef287dd11f4dc790fb76ee1c0f67

    Handle insufficient resources on accept() decently

    If accept() call fails due to insuffient OS resources
    the new connection is rejected.
Merge pull request #433 from michelp/reject-no-fds-avail

Ported from libxs revision 123c0f5387ecef287dd11f4dc790fb76ee1c0f67
Prepared for release 3.2.1
Minor documentation fix: zmq_msg_recv instead of zmq_msg_send
Merge pull request #434 from vaughan0/master

Small documentation error I noticed
Fixed issue #443
Merge pull request #435 from hintjens/master

Added ZMQ_XPUB_VERBOSE option
Renamed ZMQ_ROUTER_BEHAVIOR to ZMQ_ROUTER_MANDATORY for clarity
Merge pull request #436 from hintjens/master

Renamed ZMQ_ROUTER_BEHAVIOR to ZMQ_ROUTER_MANDATORY
commented out TOS related opt for PGM
explicit comments on multicast loopback
fixed trailing whitespace
Merge pull request #437 from rohanbedarkar/master

Explicit comments
added artificacts for windows and openpgm build
Update CMakeLists.txt

Removed check for COPYING.txt
Minor refactor of CMake build script.
Make OpenPGM a CMake option, default disabled.
Detect ZeroMQ version at build time; hide NSIS dependencies in new cmake folder.
Add metadata to CMake options; mark executables advanced to hide from default view; fix WoW64 redirections.
Detect compiler version to tag libraries.