Assertion failure in zsockopt.c:965

zsocket_set_linger: Assertion `rc == 0 ... ' failed.

Caused by using zctx_t type for global_context, so that it was trying
to shut down sockets the old way on process exit.

Solution: move global context creation/shutdown to zsys, and use plain
zmq context reference.

Note: this plus new zactor class will result in deprecated classes:
zctx, zmutex, zthread, zsocket, zsockopt.
Initial empty zactor class
Trivial comment fix
Added builds/msvc and packaging/ to source packages

Fixes #464
Allow CZMQ code to use zmq_ctx_new/term

Needs macro to backport these to libzmq/2.x
Adding zmq_ctx_init/term support for libzmq/3.x
Don't install test binaries into bindir
Merge pull request #465 from hintjens/master

Fixed #464, other changes