Problem: Tests in Travis are failing randomly

Tests were failing, because some deque calls were causing undefined
behavior: calling front() or pop_front() on an empty deque. Such
calls are now safeguarded.

Fixed missing subscriptions on XPUB with manual subscriptions

The patch fixes the issue #1568.

Problem: lingering subscriptions on XPUB sockets (#1566)

The patch fixes lingering subscriptions that occur upon disconnection
on XPUB sockets with option XPUB_MANUAL when used in a XPUB-XSUB
proxies.

Solution: do not call poller->add_fd() with -1. Fixes #1558

Revert "Solution: check return code of make_fdpair() with zmq_assert"

Make DragonFly a first class citizen in terms of compilation

Solution: check return code of make_fdpair() with zmq_assert

Cleaned up test case

Update zmq_inproc manpage for bind/connect order

The order of zmq_bind() and zmq_connect() is no longer important
for the inproc transport since libzmq 4.0.  This updates this
in the zmq_inproc manpage.

Problem: Identity frame from router has no metadata

Problem: Private/internal macros defined in public header.

Solution: Move the macros to a private header.

rename ZMQ_UNUSED macro to LIBZMQ_UNUSED

Fix zmq crash when calling shutdown with a pending inproc socket connect

Set signaler_port to 0 which allows the OS to find a free port

-Set signaler_port to 0 which allows the OS to find a free port, rather than crashing if 5905 is in use (https://github.com/zeromq/libzmq/issues/1542)
-Added config.hpp to the source list so it shows up in generated projects
-Remove CMAKE_BUILD_TYPE setting for generators that don't use it

Problem: Source files contain mixed tabs and spaces.

Solution: Convert to spaces and remove trailing whitespace in these files.

Fixes failing tests regarding XPUB sockets.

Fixes tests that were introduced in a previous pull request. See
https://github.com/zeromq/libzmq/pull/1539#issuecomment-132968987

Addresses zeromq/libzmq#1116.

This patch  adds a new member of type deque to the
xpub class that contains pointers to metadata_t.
This deque is then used (alongside pending_data
and pending_flags) to preserve metadata when
copying messages.

The routing id (identity) frame return when reading from
a router doesn't have the same metadata as the "real"
message that follows.
For example, The ZAP "User-Id" property is missing.

This patch attach the "data message"'s metadata
to the "identity message" when it is read from the router.

CI run on OSX needs binutils

problem: trying to support polling on thread safe sockets with zmq_poll failed

OSX does not ship with binutils, need to install it before the script
run via brew in order to be able to use greadelf, needed by the
qt-android CI script.

problem: new poller field in zmq_pollitem_t is changing the api