fix libzmq.pc generation under cmake

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.
fix autotools out of tree build link issue on linux

added srcdir to --version-script=$(srcdir)/libzmq.vers
Merge pull request #887 from ricnewton/master

Fix hang on terminate when inproc is connected but never bound.
Merge pull request #886 from guruofquality/auto_fixes

fix autotools out of tree build link issue on linux
Merge pull request #884 from guruofquality/cmake_fixes

fix libzmq.pc generation under cmake
Add ZMQ_MAX_SOCKETS_MAX to zmq_ctx_get()

The new options allows querying the maximum allowed number of sockets.
This is system dependent and cannot be encoded in the include file as a
preprocessor macro: for ZMQ_USE_SELECT, this depends on the FD_SETSIZE
macro at time of library compilation, not at time of include file use.
Fix a strict-aliasing with type-punning

Fixes #880
Revert "add proxy_chain, a multi proxies chaining in the same thread feature"

This reverts commit bc7441f5176589ad9a34dc2bde6b91d78a44e3e0.
Revert "add a proxy hook"

This reverts commit 9ae6a91fadb96fd48038fde04cc3d4b61b49a8a1.
fix revert
Merge pull request #891 from lalebarde/master

Reverse zmq_proxy_chain and zmq_proxy_hook
Merge pull request #890 from brunoqc/880

Fix a strict-aliasing with type-punning
Merge pull request #889 from olafmandel/MAX_SOCKETS_MAX

Add ZMQ_MAX_SOCKETS_MAX to zmq_ctx_get()
Rename ZMQ_MAX_SOCKETS_MAX to ZMQ_SOCKET_LIMIT

As per suggestion by Pieter Hintjens. Also update wording in
zmq_ctx_set manual a bit.
Merge pull request #892 from olafmandel/ZMQ_SOCKET_LIMIT

Rename ZMQ_MAX_SOCKETS_MAX to ZMQ_SOCKET_LIMIT
Update .gitignore to exclude *.exe under Cygwin
Clarify configure messages for --with-poller=...
Merge pull request #894 from olafmandel/Cygwin_gitignore

Update .gitignore to exclude *.exe under Cygwin
Merge pull request #895 from olafmandel/LIBZMQ_CHECK_POLLER

Clarify configure messages for --with-poller=...
Added temporary CURVE debugging support

- just prints server-side failures to console
- can be improved over time, e.g. enabled at build time or
  sent to inproc debug channel