update Makefile with ztree.o
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'upstream/master'
Add explicit casts for MSVC compilation
Add missing headers/implementations to msvc11 project
Zchunk - cast to byte* and remove aligned (need windows equivalent)
Prelude - define sleep as Sleep for MSVC
define S_IRUSR as _S_IREAD for MSVC

cannot pass zfile selftest after this change. no good, but it lets me
compile for now.
Added mutex locking to zctx socket list
Add zmutex to assertions to check for nullptr mutexes
Remove mutex locking in zctx_destroy
Implemented zmutex_try_lock
On failed zlist_push, unlock before zmq_close
Merge pull request #245 from ulikoehler/zctx-sync

Synchronize zctx socket list access
Merge remote-tracking branch 'upstream/master'
bugfix: leaking sockets list, sndhwm/rcvhwm not shadow copied
Merge pull request #249 from pijyoi/master

bugfixes to zctx.c
Various cleanups to zctx

* Asserts that zocket isn't null when destroying it; the tolerance for
  null sockets is a bogus workaround against corruption of zctx from
  unprotected use in multiple threads.

* Renamed 'main' to 'shadow' to make more explicit (negative property
  names are not good).

* Renamed 'socketsMutex' to 'mutex' since (a) camelCase breaks our style
  guidelines, and (b) we have one mutex to protect the object, there is
  no value in qualifying the name.

* Cleaned up constructors, the code was messy.

* All methods that modify or read zctx properties needed to be protected
  by the mutex, otherwise we'll get random outcomes.

* I still do not like the multithreaded zctx; it is incompatible with the
  current code in zthreads (e.g. we don't need shadow contexts) and is
  not sufficiently tested IMO. Also, I still don't see a valid use case
  for it.