problem: Tests are failing on windows

Problem: assertion in test_xpub_manual is swapped

Solution: check that both pointers passed as arguments to
test_missing_subscription are non-NULL, instead of the opposite.

Problem: XPUB test broken on Windows since #1569

Solution:
- Adjust test_subscriptions() to support different protocol types
- Run TCP and IPC tests everywhere but on Windows and OpenVMS

Fix unresolved external symbols for gather and scatter classes on MSVC 2010-2015.

Fix issue with unresolved external symbols for the gather and scatter classes by adding them to the MSVC 2010, 2012, 2013 and 2015 projects.

Problem: Windows IPC check broken (check_protocol)

Solution: Fix the preprocessor check from || to &&

Problem: LD search path warnings if using Clang

Solution: PR #1906 did not solve this problem properly; subsequent Travis CI
indicated that the issue happens with Clang/LLVM, so make sure to fix the
issue by detecting if Cmake CMake is using Clang for building the tests.

Problem: test_ipc_wildcard is ran on Windows

Solution: move it to the unix-only section of Makefile.am and
tests/CMakeLists.txt since it uses Unix IPC sockets.

Problem: ZMQ_SRCFD test does not work on Windows

Solution: add Winsock specific assertions, since getpeername() should will
return SOCKET_ERROR (-1) and WSAGetLastError() will be set to WSAENOTSOCK

problem: push-pull socket types are not thread safe

Problem: CMake CI does not run make test, and there is no checking for TIPC

Solution: add make test to the cmake/ci_build.sh script

Solution: add macro in ZMQSourceRunChecks.cmake and optionally
include the TIPC sources if the support is available.
More importantly, only run the TIPC tests if the support is there.

Problem: Linker search path warnings on OS X

Problem:
A per-test Linker search path was added in commit a911fa41 to CMakeLists.txt as
part of fixing Windows builds. Whilst this is silently ignored by ld(1) on
Linux, it doesn't settle well with OS X. Spurious warnings are generated about
missing directories leading to convoluted build logs.

Solution:
Make per-Test LINK_DIRECTORIES() conditional for non-Apple platforms.

Solution: try to resolve the TCP endpoint passed by the user in the
zmq_unbind call before giving up, if it doesn't match.
This fixes a breakage in the API, where after a call to
zmq_bind(s, "tcp://127.0.0.1:9999") with IPv6 enabled on s would
result in the call to zmq_unbind(s, "tcp://127.0.0.1:9999") failing.
Add more test cases to increase coverage on all combinations of TCP
endpoints.

Solution: add one test run in a docket container environment, which
is currently the only environment where it's possibile to bind a
socket to ::1.

Solution: add helper function is_ipv6_available to testutil.hpp to
test if IPv6 is available on the building platform.
This function will try to open and bind a socket to ::1:*, as it's
the ultimate way of knowing if, at least on the loopback, IPv6 is
enabled.

Problem: comment not well formed in CMakeLists.txt

Solution: fix comment

Problem: test_udp does not release resources properly

Solution:
- call zmq_msg_close() if there is an error
- call free() to release resources if there is an error (CWE-404)

Problem: check_protocol() logic duplicated twice and needs cleanup

Problem:
Conditional logic in check_protocol() that checks if a protocol is supported,
is duplicated twice. Moreover, the first set of checks to ascertain if a
protocol is supported is done regardless of whether the particular protocol
will be built into the library or not.

Solution:
* Simplify/collapse all supported protocol checks into one in check_protocol()
* Enclose pgm/epgm/norm socket+protocol match checks with requisite macros

Problem: errno not set if UDP is NOT used with ZMQ_RADIO or ZMQ_DISH

Solution: set errno to ENOCOMPATPROTO in check_protocol()

Problem: Running Linux-only tests results in 10% of tests failing on non-Linux systems (OSX, et. al.)

Move tests specific to Linux under a platform conditional thereby eliminating
unnecessary builds and fixing "make test" on Mac OS X and possibly other
non-Linux systems.

Tests specific to Linux:
    - abstract namespace support for AF_UNIX sockets
    - TIPC support (AF_TIPC)

Test success rate jumps from 90% to 100% on Mac OS X after this change.