https://zeromq.jira.com/browse/LIBZMQ-565

Terminate context in a child process of fork() to replace file descriptors to not interfere with parent process's context

Copyrights had become ads for Sustrik's corporate sponsors, going against the original
agreement to share copyrights with the community (that agreement was: one line stating
iMatix copyright + one reference to AUTHORS file). The proliferation of corporate ads
is also unfair to the many individual authors. I've removed ALL corporate title from
the source files so the copyright statements can now be centralized in AUTHORS and
source files can be properly updated on an annual basis.

Significantly reworked the monitoring infrastructure with a more granular per socket API and to play well with monitoring endpoints in application threads

There are three versions of monitor_event(), all taking
variadic arguments. The original code just has the first one
creating a va_list and passing that va_list variadically to
the second one... which creates a new va_list and passes it
variadically to the third one... and of course everything
blows up when we try to pull a non-va_list argument off the
stack.

The correct approach matches the C standard library's use
of printf/vprintf, scanf/vscanf, and so on. Once you make
a va_list, you must pass it only to functions which expect
a va_list parameter.

* corrects whitespace errors
* fixes spelling errors in comments
* prefers #ifdef to #if defined

* Implemented new ctx API (_new, _destroy, _get, _set)
* Removed 'typesafe' macros from zmq.h
* Added support for MAX_SOCKETS (was tied into change for #337)
* Created new man pages

We use a distinct context initialisation function to specify
all sockets derived therefrom will be thread safe.

However the inheritance is done exclusively in the C interface.
This is not really correct, but it is chosen to minimise
interference with the existing C++ code, including any
construct or other calls within the C++ code base.
Semantically the C++ code should be unchanged,
physically some data structures and extra methods are
provided by they're only used from the C binding.

Older versions of gcc have problems with in-line forward declarations
when there's a naming conflict with a global symbol.
Signed-off-by: AJ Lewis <aj.lewis@quantum.com>

Expand the original patch to all such forward declarations.
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

The class was not used anywhere anymore. Removed.
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

This patch addresses serveral issues:
1. It gathers message related functionality scattered over whole
   codebase into a single class.
2. It makes zmq_msg_t an opaque datatype. Internals of the class
   don't pollute zmq.h header file.
3. zmq_msg_t size decreases from 48 to 32 bytes. That saves ~33%
   of memory in scenarios with large amount of small messages.
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

Reaper thread destroys the socket asynchronously.
zmq_term() can be interrupted by a signal (EINTR).
zmq_socket() will return ETERM after zmq_term() was called.
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

The meat of the patch was contributed by Douglas Creager.
Martin Sustrik implemented storing peer options in inproc
endpoint repository.
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

For historical reasons queue to transfer commands between
threads was called 'signaler'. Given that it was used to
pass commands rather than signals it was renamed to 'mailbox',
see Erlang mailboxes.
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

Threads were so far identified by integers called 'slots'.
This patch renames them to more comprehensible 'tid's (thread IDs).
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>