Solution: Phase I - make precompiled.hpp be first file included in every source file

Solution: always initialised zmq::options_t class variables arrays to
avoid reading uninitialised data when CURVE is not yet configured and
a getsockopt ZMQ_CURVE_{SERVER | PUBLIC | SECRET]KEY is issued.

It's unclear which we need and in the source code, conditional code
treats tweetnacl as a subclass of libsodium, which is inaccurate.

Solution: redesign the configure/cmake API for this:

* tweetnacl is present by default and cannot be enabled
* libsodium can be enabled using --with-libsodium, which replaces
  the built-in tweetnacl
* CURVE encryption can be disabled entirely using --enable-curve=no

The macros we define in platform.hpp are:

    ZMQ_HAVE_CURVE    1        //  When CURVE is enabled
    HAVE_LIBSODIUM    1        //  When we are using libsodium
    HAVE_TWEETNACL    1        //  When we're using tweetnacl (default)

As of this patch, the default build of libzmq always has CURVE
security, and always uses tweetnacl.

These options are confusing and redundant. Their names suggest
they apply to the tcp:// transport, yet they are used for all
stream protocols. The methods zmq::set_tcp_receive_buffer and
zmq::set_tcp_send_buffer don't use these values at all, they use
ZMQ_SNDBUF and ZMQ_RCVBUF.

Solution: merge these new options into ZMQ_SNDBUF and ZMQ_RCVBUF.

This means defaulting these two options to 8192, and removing the
new options. We now have ZMQ_SNDBUF and ZMQ_RCVBUF being used both
for TCP socket control, and for input/output buffering.

Note: the default for SNDBUF and RCVBUF are otherwise 4096.

Solution: rename to ZMQ_MAXRT

This is the option name used on Windows, so easier to use and
remember.

Solution: rename socket option (and variables and files) from usefd
to use_fd.

Solution: rename socket option (and variables and files) from
pre_allocated_fd to usefd.

Otherwise, it's undefined behavior. ubsan catches alignment issues in
the libzmq test suite without this.

There's no value in this as the same pattern is repeated in several
places and it's fair to expect people to understand it.

Solution: revert to the old, one-liner style.

It's undefined behavior, and ubsan flags it.

Solution: add new [set|get]sockopt ZMQ_PRE_ALLOCATED_FD to allow
users to let ZMQ use a pre-allocated file descriptor instead of
allocating a new one. Update [set|get]sockopt documentation and
test accordingly.

The main use case for this feature is a socket-activated systemd
service. For more information about this feature see:
http://0pointer.de/blog/projects/socket-activation.html

- zmq_utils.h was removed
- udp_address.cpp and udp_engine.cpp were added

Solution: patch all affected build scripts

This commit addresses the following warnings reported on gcc 5.2.1. In
the future, this will help reduce the "noise" and help catch warnings
revealing a serious problem.

8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---
/path/to/libzmq/src/options.cpp:1048:36: warning: unused parameter ‘option_’ [-Wunused-parameter]
 bool zmq::options_t::is_valid (int option_) const
                                    ^

/path/to/libzmq/src/plain_client.cpp:146:30: warning: unused parameter ‘cmd_data’ [-Wunused-parameter]
         const unsigned char *cmd_data, size_t data_size)
                              ^

/path/to/libzmq/src/plain_client.cpp:146:30: warning: unused parameter ‘cmd_data’ [-Wunused-parameter]
         const unsigned char *cmd_data, size_t data_size)
                              ^

/path/to/libzmq/src/socket_base.cpp:1445:44: warning: unused parameter ‘group_’ [-Wunused-parameter]
 int zmq::socket_base_t::xjoin (const char *group_)
                                            ^
/path/to/libzmq/src/socket_base.cpp:1451:45: warning: unused parameter ‘group_’ [-Wunused-parameter]
 int zmq::socket_base_t::xleave (const char *group_)
                                             ^

/path/to/libzmq/src/radio.cpp:145:33: warning: unused parameter ‘msg_’ [-Wunused-parameter]
 int zmq::radio_t::xrecv (msg_t *msg_)
                                 ^
/path/to/libzmq/src/dish.cpp:164:32: warning: unused parameter ‘msg_’ [-Wunused-parameter]
 int zmq::dish_t::xsend (msg_t *msg_)
                                ^

/path/to/libzmq/tests/test_msg_ffn.cpp:32:16: warning: unused parameter ‘data’ [-Wunused-parameter]
 void ffn(void *data, void *hint) {
                ^

/path/to/libzmq/tests/test_timers.cpp:50:19: warning: unused parameter ‘timer_id’ [-Wunused-parameter]
 void handler (int timer_id, void* arg)
                   ^
8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---

Solution: update to 2016

VMCI transport allows fast communication between the Host
and a virtual machine, between virtual machines on the same host,
and within a virtual machine (like IPC).

It requires VMware to be installed on the host and Guest Additions
to be installed on a guest.

Fixes #1646

Solution: change option behaviour and adopt documentation

Solution: make tcp_recv_buffer_size and tcp_send_buffer_size unsigned

Solution: make base a double value

Fixed ZMQ_TCP_RECV_BUFFER set case.

LIBZMQ-195 allow explicitly setting sndbuf and rcvbuf to 0 (see https://support.microsoft.com/en-us/kb/201213)

Set the ZMQ_HEARTBEAT_TIMEOUT to default to the value of
ZMQ_HEARTBEAT_IVL if it's not explicitly set.
Change the units of ZMQ_HEARTBEAT_TTL to milliseconds in the API
and round down to the nearest decisecond so that all the options
are using the same units.
Make the maximum heartbeat TTL match the spec (6553 seconds)

This commit adds ZMTP connection heartbeats described in
http://rfc.zeromq.org/spec:37/ZMTP.

Of course people still "can" distributed the sources under the
LGPLv3. However we provide COPYING.LESSER with additional grants.

Solution: specify these grants in the header of each source file.

ZMQ_INVERT_MATCHING reverses the PUB/SUB prefix matching. The subscription
list becomes a rejection list. The PUB socket sends messages to all
connected (X)SUB sockets that do not have any matching subscription.

Whenever the option is used on a PUB/XPUB socket, any connecting SUB
sockets must also set it or they will reject everything the publisher
sends them. XSUB sockets are unaffected because they do not filter out
incoming messages.

Symptom is that ZMQ_STREAM sockets in 4.1.0 and 4.1.1 generate zero
sized messages on each new connection, unlike 4.0.x which did not do
this.

Person who made this commit also changed test cases so that contract
breakage did not show. Same person was later banned for persistently
poor form in CZMQ contributions.

Solution: enable connect notifications on ZMQ_STREAM sockets using a
new ZMQ_STREAM_NOTIFY setting. By default, socket does not deliver
notifications, and behaves as in 4.0.x.

Fixes #1316

Solution: update for 2015

Fixes #1320

Solution: set defaults back to infinity, and add new context
option, ZMQ_BLOCKY that the user can set to false to get a
less surprising behavior on context termination. Eg.

    zmq_ctx_set (ctx, ZMQ_BLOCKY, false);

Regression in #1248 can cause lost messages at exit.

Solution: use a sane value, e.g. 2 seconds

Fixes #1247