Solution: added to test_stream.cpp

fix: ZMQ_TCP_RETRANSMIT_TIMEOUT not applied to bind socket

Avoid terminating connections prematurely

While sending very large messages (far beyond what fits in a the tcp
buffer, so it takes multiple sendto system calls for it to finish),
zmq_close will close the connection regardless of ZMQ_LINGER.

In case no engine is attached, a pipe->check_read() is needed to look
for the delimiter in the pipe and ultimately trigger the pipe
termination.

However, if there *is* an engine attached, the check_read() looks ahead
and finds the delimiter and terminates the connection even though the
engine might actually still be in the middle of sending a message.

This happens because while the io_thread is still busy sending the data,
the pipe can get terminated and the io thread ends up being terminated.

add ZMQ_TCP_RETRANSMIT_TIMEOUT socket option

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.