In real world usage, there have been reported signaler failures where the
eventfd read() or socket recv() system call in signaler::recv() fails,
despite having made a prior successful signaler::wait() call.

this patch creates a signaler::recv_failable() method that allows
unreadable eventfd / socket to return an error without asserting.

I had the assertion below fail occasionally when running the libzmq
tests under heavy CPU load on linux 3.16.0-4-amd64.

Previously, AddressSanitizer flagged leaks when running
tests/test_many_sockets.cpp.

Of course people still "can" distributed the sources under the
LGPLv3. However we provide COPYING.LESSER with additional grants.

Solution: specify these grants in the header of each source file.

This is a silly assertion that causes problems if libzmq.dll is
called in some esoteric ways.

Solution: if the shutdown code detects WSANOTINITIALISED, then
exit silently.

Fixes #1377
Fixes #1144

Solution: update for 2015

Fixes #1320

Updated:
    src/signaler.cpp: Add close_wait_ms() static function to loop
       when receiving EAGAIN in response to close(), with ms long
       sleeps, up to a maximum limit (default 2000ms == 2 seconds);
       used in signaler_t::~signaler_t() destructor.

* report from Richard Newton indicated previous solutions was not
  working on Windows

The decision about the poller mechanism to use (select, poll, ...)
was done twice: once by the build system and once by the code in
poller.hpp. As the build-system can actually detect the mechanisms
available, prefer that result to the hard coded defaults in
poller.hpp.

At the same time, remove the duplicate detection of select() vs.
poll()-variant from proxy.cpp, signaler.cpp and zmq.cpp.

This patch has not been tested on many build platforms: especially
the cmake build needs testing / patching. For the other builds,
hard code the result as these these are all Windows platforms.

the size of the critical section is reduced by only entering the critical
section right before the bind().

Update signaler make_fdpair to set file descriptors to -1 when too many files are open using socketpair.

Fix socket creation above sistem limits for all 'other' OS not covered by eventfd, windows or vms; enhanced test to create sockets up to a bigger limit to really test hitting the OS limit

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.

- Windows CE does not manage security attributes (no SetSecurityDescriptorDacl(), SetEvent (NULL, xxx) ...)
- Windows CE does not inheritance of sockets for child process (SetHandleInformation ((HANDLE) *w_, HANDLE_FLAG_INHERIT...)
- see comments about story "Porting ZeroMQ to Windows Mobile" on webpage http://www.zeromq.org/story:5

TIME_WAIT state.