Problem: Since pull request #1730 was merged, protocol for REQ socket is
checked at the session level and this check does not take into account
the possibility of a request_id being part of the message. Thus the option
ZMQ_REQ_CORRELATE would no longer work.
This is now fixed: the possiblity of a 4 bytes integer being present
before the delimiter frame is taken into account (whether or not this
breaks the REQ/REP RFC is another issue).

Fixes #1419 segfault when using a XSUB/XPUB proxy.

Ref. https://github.com/zeromq/libzmq/issues/1419

Windows XP compatability fixes

A Visual Studio build from master (commit id: dac5b45d) using the v140_xp toolset yields a binary that is not XP compatible.

Two libraries contain exports that cannot be found:
 -  IPHLPAPI.DLL : if_nametoindex
 - KERNEL32.DLL : InitializeConditionVariable

The latter export is already dealt with in the file './src/condition_variable.hpp'; however this requires setting the _WIN32_WINNT pre-processor definition.
I am not experienced enough to figure a work around for the 'if_nametoindex' method, so I have created a new pre-processor definition 'ZMQ_HAVE_WINDOWS_TARGET_XP' and removed the calling of the function with the limitation that these builds cannot handle a IPv6 address with an adapter name.

To make it easier for people targeting XP with an MSVC build I have modified the MSBuild property file to add/modify the pre-processor definitions if they are building using a XP targeting tool set; such as v140_xp.

Improve MSVC builds

* Added a new .gitignore file for excluding Visual Studio build output any popular plug-in generated content. (This was copied from the GitHub project https://github.com/github/gitignore).
* Removed the basic ignore settings from the root folder in favour of more precision within the subfolder's .gitignore file
* Added the new VC compiler's experimental Intellisense database file

All the older (vs2010 -> vs2013) projects had copies of the Visual Studio 2015 MSBuild applied to them when running the 'configure.bat' batch file. Any modifications to a property sheet was not applied to the other Visual Studio versions' projects unless the batch file was re-executed.

* Modified the older projects to reference the Visual Studio 2015 property sheets so changes are immediately applied
* Removed the batch file copy steps (which left the repository very dirty after execution)

Tweaks to building libzmq

I changed this to ZMQ_USE_SODIUM to be consistent with other
configuration options (especially ZMQ_USE_TWEETNACL).

Solution: fix it.

Tweaks to building libzmq

Solution: update them.

Solution: use ZMQ_USE_LIBSODIUM to match ZMQ_USE_TWEETNACL

Problem: build fails when CURVE security is disabled

Solution: use proper preprocessor macro

Problem: CURVE mechanism is unusable with chroot()

libsodium calls abort() when /dev/urandom can't be found
even if one creates ZeroMQ context before calling chroot()[1].

This happens because crypto gets initialized on handshake,
and at that moment the process is already chroot'ed.

Solution: initialize cryptographic libraries in ctx

randombytes_close() is already there in the destructor.

[1] https://download.libsodium.org/doc/usage/index.html

Update zmq_utils.h

Previous change broke MSVC b/c MSVC doesn't support #warning

zeromq-4.1.4/src/tcp_address.cpp : fix relaxed use of sizeof() without parenthesis

Fixed issue #1695 (ZMQ_REQ_CORRELATE)

Problem: when using ZMQ_REQ_RELAXED + ZMQ_REQ_CORRELATE and two 'send' are
executed in a row and no server is available at the time of the sends,
then the internal request_id used to identify messages gets corrupted and
the two messages end up with the same request_id. The correlation no
longer works in that case and you may end up with the wrong message.

Solution: make a copy of the request_id instance member before sending it
down the pipe.

Add Valgrind make target and CI run

Solution: pass built-root when calling coveralls, to help it find the
right path to the source code.

Solution: run Travis CI in newer Trusty (14.04 LTS) release.

Solution: do not run test_fork if --enable-valgrind is set. Note that
later versions of Valgrind (3.11) not yet available in all
distributions fix this problem, so we might revert in the future.

Solution: update builds/valgrind/valgrind.supp to ignore glibc's
__libc_freeres calls. This code runs after the program exits, and
tries to de-allocate memory allocated internally by glibc, so it has
nothing to do with libzmq code. This suppression is added by default
in newer versions of Valgrind, not yet available on older
distributions.

Solution: run Valgrind only on the default Linux build to avoid
increasing the runtime.

Solution: import ax_valgrind_check.m4 macro file to provide a
conveniente automake hook to run Valgrind on all tests.
Add --enable-valgrind to ./configure call and then run make
check-valgrind to run memcheck, helgrind, drd and sgcheck on all
tests. Run check-valgrind-memcheck to run only memcheck.

Fix usage of IPv6 addresses

Problem: test_large_msg requires 2GB of free RAM

Use FILENAME_MAX to determine BUFSIZE when getting socket path.

Solution: remove temporarily until proper message limits have been
implemented, then a more granular test case can be added without
such high requirements which are problematic in embedded environment,
build systems, VMs and CI systems

Problem: IPC wildcard test broken on OSX