Problem: code isn't setting mechanism to CURVE properly

Stop ZMTP handshake when an unexpected message comes

Clean up socket_type_string

API for CURVE configuration

Changes to sanity tag in ctx

Ignored more MSVC intermmediate files.

- ZMQ_CURVE_PUBLICKEY for clients and servers
- ZMQ_CURVE_SECRETKEY for clients
- ZMQ_CURVE_SERVERKEY for clients
- ZMQ_CURVE_SERVER for servers
- added tools/curve_keygen.c as example
- updated man pages

Implement ZMTP/3.0 CURVE handshake

Missing files in cmake generated build.

fix memory leak in ipc_listener wildcard

another iteration on ZMQ_PROBE_ROUTER

now it properly works for ROUTER

Updated ZAP PLAIN request to follow latest draft

- username and password sent as two string frames
- fixed test case to match

- REQ and REP sockets don't have HWM issues
- ZMQ_DONTWAIT applies to DEALER and PUSH only

Add ZAP support

Packaging of probe function

- renamed to ZMQ_PROBE_ROUTER

- Cleaned up man page a little
- Wrote test case tests/test_router_probe.cpp

implement it for DEALER tocket.
+documentation

Make "./configure --with-system-pgm" detect the OpenPGM 5.2 system library.

    ./configure --with-system-pgm
detect the OpenPGM 5.2 system library.

Note that OpenPGM installs a versioned pkgconfig file
(openpgm-5.2.pc, openpgm-5.1.pc).

Fold constant expression into constant.

Fixed memory leak in stream engine

Refactoring of 'ZMQ_ROUTER_ANNOUNCE_SELF'