Fix zmq_socket example in documentation

Issues adressed:
 - The actual data was never read from the socket, causing all even
   numbered loop iterations to fail
 - The socket variable was called server once
Merge pull request #904 from olafmandel/zmq-socket.man

Fix zmq_socket example in documentation
add linking to librt under cmake build - fixes missing symbol

The libzmq library itself uses clock_gettime and should link w/ -lrt on linux.
Caught this issue on on Ubuntu 12.04 LTS.
Merge pull request #905 from guruofquality/missing_librt

add linking to librt under cmake build - fixes missing symbol
Fix MSVC8 build

The extra semicolons were introduced in 48b50ce together with the
defintion of the ZMQ_USE_SELECT macros.
Merge pull request #906 from olafmandel/fix_msvc8_build

Fix MSVC8 build
Added scaffolding for zmq_msg_gets
Merge pull request #910 from hintjens/master

Added scaffolding for zmq_msg_gets
Minor change to zmq_curve_keypair doc
Merge pull request #911 from KennethWilke/master

Minor change to zmq_curve_keypair doc
Libsodium is now required if and only if --with-libsodium is used

This patch is proposed for https://github.com/zeromq/libzmq/issues/912.  If a user specifies that they want libzmq built with libsodium, and the requirement cannot be satisfied, we should error at the user so they can either A) install libsodium to a reasonable location or B) relax their requirement for libsodium support.

Previously a warning was issued in this case, causing users who wanted libsodium support not to get it, which may be discovered at a much later time when their programs didn't work as expected.

I release this patch under the LGPL v3 or any later version.
Merge pull request #914 from drewcrawford/issue_912

Libsodium is now required if and only if --with-libsodium is used
Add the tag name to the zmq_pollitem_t struct to allow easier forward declaration
Merge pull request #920 from mbarbisan/master

Add the tag name to the zmq_pollitem_t struct to allow easier forward de...
Allow TCP addresses to be re-resolved whenever there is a reconnection attempt
Merge pull request #921 from mbarbisan/master

Allow TCP addresses to be re-resolved whenever there is a reconnection a...
Fixed potential SEGFAULT.
Merge remote-tracking branch 'upstream/master'
Merge pull request #922 from horus42/master

Fixed potential SEGFAULT in socket_base.cpp
Revert "Fixed potential SEGFAULT."

This reverts commit 79b81f48402c1276d4cfd3bf0cbfb4084952b36b.
Was causing:

Assertion failed: destroyed (socket_base.cpp:154)
/bin/bash: line 5: 31344 Aborted                 ${dir}$tst
FAIL: test_many_sockets

On TravisCI.