This became necessary after 22d6a974

fork() support is optional and its availability is correctly detected at
contfigure time.

But test_fork was all always built, preventing build for targets that do
not provide fork() from building successfully.

This pacth fixes the CMakeLists.txt on this point.

* was problem on debian/wheezy

The libzmq library itself uses clock_gettime and should link w/ -lrt on linux.
Caught this issue on on Ubuntu 12.04 LTS.

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 ${libdir} was getting replaced/removed by configure_file() making pkg-config give bad flags: -L -lzmq
My fix was to add @ONLY to configure_file() so ${} style pkg-config substitutions are left alone.
In addition, I put the other typical ${} substitutions back into the libzmq.pc, since its now safe.

Added ZMQ_BUILD_TESTS to CMakeLists.txt to allow turning off tests. Useful when building ZMQ as a git submodule.

File was removed in 5bf96f64 a few days ago.

When a ZMQ_STREAM socket connection is broken (intentionally, via `shutdown()`
or accidentally via client crash or network failure), there is no way for the
application to dertermine that it should drop per-connection data (such as
buffers).

This contribution makes sure the application receives a 0-length message to
notify it that the connection has been broken.  This is symmetric with the
process of closing the connection from within the application (where the
application sends a 0-length message to tell ZeroMQ to close the connection).

Conflicts:
	CMakeLists.txt

Another take on LIBZMQ-568 to allow filtering IPC connections, this time
using ZAP.  This change is backward compatible.  If the
ZMQ_ZAP_IPC_CREDS option is set, the user, group, and process IDs of the
peer process are appended to the address (separated by colons) of a ZAP
request; otherwise, nothing changes.  See LIBZMQ-568 and zmq_setsockopt
documentation for more information.

See https://github.com/zeromq/issues/pull/7Signed-off-by: Shannen Saez <shannenlaptop@gmail.com>

This reverts commit 0b92831b.