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

Solution: increase path buffer length to 73

Update Unix Domain Socket creation/handling

Updated handling of Unix Domain Sockets, make use of temporary directories, and cleanup afterward.  Fix test_term_endpoint handling of optvallen

Add code coverage to build system and CI

Solution: add it

Solution: add new coverage build, and upload results to coveralls.io

Solution: import ax_code_coverage.m4 from autoconf-archive and use it
in configure.ac and Makefile.am in order to provide a make
check-code-coverage target behind a --enable-code-coverage configure
flag, that can be used to generate a gcov/lcov code coverage report.
Depends on having gcov and lcov installed.

Problem: Windows PDB not created for RELEASE targets

Solution: Modified projects to create PDB file for RELEASE targets
	- also spread precompiled settings to all DevStudio solution versions

This change affects Windows builds only

parameter naming consistency [aesthetic]

Problem: make dist does not tar up macros.hpp

Better comments for understanding the classes array_t<> and array_ite…

Solution: run make dist-check, which will run additional tests,
including making sure that the library is installable and the
distributable tarball is buildable, along with the usual make and
make check.

Solution: simply run make VERBOSE=1 check instead of manually
checking for return value and cat'ing the log file. With VERBOSE, on
error the log file will be automatically printed.

Solution: add the document files to the MAN_DOC and MAN_HTML targets
in doc/Makefile.am only if BUILD_DOC and INSTALL_MAN are set,
otherwise leave the targets empty to avoid errors in make distcheck.

Solution: add it to Makefile.am file list

Problem: CMakelist missing support for Windows Precompiled headers

Solution: Add precompiled flags to CMakeList.txt for faster compiles
+ bonus - removed compilation warning on Windows by adding
	 add_definitions (-D_WINSOCK_DEPRECATED_NO_WARNINGS)

Problem: Tests do no build in Windows environment