Fixes #872

Added ZMQ_BUILD_TESTS to CMakeLists.txt to allow turning off tests. 

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

Fix potential segfault/memleak

Delete the socket if the initialization part of the socket creation
fails.

Call the allocation assertion macro before dereferencing the socket
pointer.

Fixed issue #868

Fixed issue #865 - validation on ZMQ_TCP_KEEPALIVE

Fix cmake build

Test for 127.0.0.1 at tests startup

Fixed man page for zmq_proxy_hook

- spaces instead of tabs for indentation
- fixed levels under EXAMPLE USAGE
- added to Makefile.am

[libzmq] const string p -> const string& p (#860)

add proxy_chain, a multi proxies chaining in the same thread feature

Man page fixes

add a proxy hook

Fixes to test cases

- renamed test_stream_disconnect_notifications (too long!)
- removed print statements in that test case
- fixed Makefile.am for test_zap_ipc_creds (was not building)

typo fix: RECVHWM -> RCVHWM

Changed fail behavior of CONNECT_RID to an assert failure instead of silent failure.

Added assert on duplicate id in ROUTER and STREAM sockets.  Updated man to reflect this change.  Modified test case to match.

Cleaned up formatting of test_connect_rid.  Set LINGER to 0 on sockets.  This may address the test failing on some devices.

factorize code in proxy

Added test_connect_rid