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

Solution: Modified CMakelist.txt to build correctly for Windows
- corrected CMake required version to make sure it builds in
  Ubuntu 14.04 LTS with no warnings.

Solution: Modified CMakelist.txt to build correctly for Windows

Problem: Windows Build not using precompiled headers for all targets

Problem: Added "make clean" to Windows build scripts

Solution: Enabled precompiled header settings in all targets
Before build time: ~6min 49 secs
Stop  Time: Fri 03/04/2016  8:29:50.13
Start Time: Fri 03/04/2016  8:23:00.28

After build time: ~4min 19 secs
Stop  Time: Fri 03/04/2016 12:12:10.24
Start Time: Fri 03/04/2016 12:07:51.78

Solution: Added ability to do equivalent of a "make clean" by executing:

O:\git\libzmq\builds\msvc\build>buildall.bat clean
Start Time: Fri 03/04/2016 14:33:56.50
Cleaning without libsodium
Cleaning ..\vs2013\libzmq.sln... ()
Platform=x86
Configuration=DynDebug
Configuration=DynRelease
Configuration=LtcgDebug
Configuration=LtcgRelease
Configuration=StaticDebug
Configuration=StaticRelease
Platform=x64
Configuration=DynDebug
Configuration=DynRelease
Configuration=LtcgDebug
Configuration=LtcgRelease
Configuration=StaticDebug
Configuration=StaticRelease
Cleaning complete: ..\vs2013\libzmq.sln

Stop  Time: Fri 03/04/2016 14:34:01.84
Start Time: Fri 03/04/2016 14:33:56.50

A clean takes ~5 secs to complete.

Problem: Visual Studio Toolset was incorrectly set in VCXPROJ files

Problem: Fix C++ style comment usage in C source

Problem: Fix unportable `==` operator for `test`

Problem: Fix build with Heimdal krb5

Solution:
* Check gssapi/gssapi_generic.h header file, it is not in Heimdal.
* Check libgssapi too, libgssapi_krb5 is not separated in Heimdal.

minor automake fixes plus tweetnacl logic change

Brackets around defaults in configure --help strings for
--with-libsodium and --disable-curve were not displayed.

Solution:  Add m4 quotes.

Move AM_CONDITIONAL for --disable-curve outside of shell
conditional (per sec 20.1 of automake manual) and fix its
second argument to be a test rather than a literal zero.

Problem: can't be sure crypto_box always returns 0

Libsodium has started returning -1 in some cases.

Solution: allow and handle error returns from these calls.

Fixes #1831

include sys/ucred.h for struct ucred

Platforms that have struct ucred, typically declare it in sys/ucred.h

update Makefile.mingw32

Problem: make dist is borken

Solution: add it to .gitignore

Solution: change builds/msvc/Makefile.am to reference vcxproj files
instead of props files.

Solution: change builds/Makefile.am to reference builds/android
instead of builds/qt-android.

Solution: remove references to builds/cmake/Makefile* since they no
longer exist.

Solution: socket_base_t::in_event cannot do anything useful with
return status of process_commands. Asserting is the wrong solution,
as it is entirely valid to be interrupted or for the context to be
terminated, so discard the value.