add ZMQ_CONNECT_TIMEOUT option

ZMQ_TCP_KEEPALIVE_IDLE doc wrongly mentions TCP_KEEPCNT

was fixed in zmq_setsockopt.txt but not in zmq_getsockopt.txt

Increase file limit in travis config

Test cases occasionally fail, especially on OSX, due to socket limit.
Part of fix for #1502

Travis ci osx

ldconfig is not available on OSX, so Travis CI build fails

readelf is not available on OSX, greadelf is available on homebrew

Remove type-pun in zmq.cpp to resolve issue #1500.

Documentation fixes for socket options.

ZMQ_TCP_KEEPALIVE_IDLE doc wrongly says it overrides TCP_KEEPCNT

Check for libtoolize instead of libtool on Linux

autogen.sh has a check for the libtool binary as a mean to
check if libtool is available. But distributions like Debian and
Ubuntu are splitting the libtool package, and the libtool binary is now
in a separate package. What autoconf actually need is not the libtool
binary, but libtoolize and other macro files. So check for libtoolize
instead. On the other hand, OSX only ships libtool, not libtoolize,
and uses a pre-generated libtool script to build. So check for
libtoolize first and then for libtool, and fail if neither can be
found.

Add a way to disable libzmq's internal test timeout.

Increase sleep in test to fix flakiness under CPU load.

Retry recv if it only returns part of a message during tests.

Fix test flakiness.

Fix a documented memory leak.

Fix eventfd read handling under heavy load.

Under linux 3.16.0-4-amd64, I was getting occasional test failures
before fixing this.

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

I'm pretty sure this is an issue with the test being too picky and not a
bug, but the behavior in this situation is not well documented.

Despite the old comments, re-initing the msg_t leaks a refcount to
metadata in some situations.

v1_decoder looks like it isn't tested any more, but it seems like a good
idea to fix it because it has the exact same piece of buggy code
v2_decoder does.

It's nice to be able to disable libzmq's internal timeout when there's
another timeout in the test runner being used which gives nicer error
messages.

Problem: VS builds missing files, have warnings.