Fix issue #370

The patch extends the internal session's API with the reset method.
This method is used to reset a session's state so that it can
handle a new connection.

Code cleanup

Fix issue #369

The bug was that after reconnect, the session did not
handle identity messages properly.

Fixed zmq_poll.txt manpage for issue #361

Code cleanup

Fix too long underline in zmq_ctx_set_monitor() docs

Rename monitor documentation source file to match zmq_ctx_set_monitor() API

Moves the monitoring infrastructure to a global zmq_ctx_set_monitor () API to avoid strict aliasing issues with function pointers and socket options.

Fixed bogus reference to zmq_ctx_put

Doc improvement: document interface omission in zmq_pgm.txt

Solaris/SunCC build fix: could not find a match for std::multimap<...>::insert(std::pair<...,...>)

The PGM transport supports the omission of the network interface to
select the default one like:

  announce.connect("epgm://eth0;239.255.128.46:64646"); // Use eth0
  announce.connect("epgm://239.255.128.46:64646"); // Use the default

Also, mention C++ in the additional community bindings of 0MQ in
zmq.txt.

Rename type zmq_monitor_fn -> zmq_monitor for a more natural callback definition API (zmq_monitor type, monitor.function callback)

Change zmq_monitor_fn type to cast between pointer-to-object and pointer-to-function in a more standards compliant way

Allow the ZMQ_MONITOR code compilable on gcc 4.7 on Linux.

The current ZMQ_MONITOR code does not compile in gcc 4.7, as -pedantic
and -Werror are enabled, and ISO C++ doesn't allow casting between
normal pointers (void*) and function pointers, as pedantically their
size could be different. This caused the library not compilable. This
commit workaround the problem by introducing one more indirection, i.e.
instead of calling

    (void *)listener

which is an error, we have to use

    *(void **)&listener

which is an undefined behavior :) but works on most platforms

Also, `optval_ = monitor` will not set the parameter in getsockopt(),
and the extra casting caused the LHS to be an rvalue which again makes
the code not compilable. The proper way is to pass a pointer of function
pointer and assign with indirection, i.e. `*optval_ = monitor`.

Also, fixed an asciidoc error in zmq_getsockopt.txt because the `~~~~`
is too long.

Expose a ZMQ_MONITOR socket option to register a callback for notification of state changes in socket state ( stream engine, tcp and ipc transport only )