This reverts commit d4bb6d69.

This reverts commit e7804c50.

* Added new man page for this
* Added test case, in tests/test_security_curve.cpp
* Noted in zmq_utils.h that these methods are documented

they are used by curve_keygen, but not available

* ZMQ_REQ_STRICT was negative option (default 1) which goes against
  the standard, where defaults are zero. I renamed this to
  ZMQ_REQ_RELAXED.

* ZMQ_REQ_REQUEST_IDS felt clumsy and describes the technical solution
  rather than the problem/requirement. I changed to ZMQ_REQ_CORRELATE
  which seems more explicit.

This reverts commit bfd472f9.

This reverts commit 1206f457.

* Removed redundant Z85 code and include files from project
* Simplified use of headers in test cases (now they all just use testutil.hpp)
* Export zmq_z85_encode() and zmq_z85_decode() in API
* Added man pages for these two functions

* This is passed to the ZAP handler in the 'domain' field

* If not set, or empty, then NULL security does not call the ZAP handler

* This resolves the phantom ZAP request syndrome seen with sockets where
  security was never intended (e.g. in test cases)

* This means if you install a ZAP handler, it will not get any requests
  for new connections until you take some explicit action, which can be
  setting a username/password for PLAIN, a key for CURVE, or the domain
  for NULL.

- Split off NULL security check from PLAIN
- Cleaned up test_linger code a little
- Got all tests to pass, added TODOs for outstanding issues
- Added ZAP authentication for NULL test case
- NULL mechanism was not passing server identity - fixed
- cleaned up test_security_plain and removed option double-checks (made code ugly)
- lowered timeout on expect_bounce_fail to 150 msec to speed up checks
- removed all sleeps from test_fork and simplified code (it still passes :-)

It defaults to enabled. Switch it off to be able to send a new message
before the previous reply has been received.

This allows making a new request on a REQ socket by sending a new
message. Without the option set, calling send() after the first message
is done will continue to return an EFSM error.

It's useful for when a REQ is not getting a response. Previously that
meant creating a new socket or switching to DEALER.

* Documentation:
The default behavior of REQ sockets is to rely on the ordering of messages
to match requests and responses and that is usually sufficient. When this option
is set to 1, the REQ socket will prefix outgoing messages with an extra frame
containing a request id. That means the full message is (request id, 0,
user frames...). The REQ socket will discard all incoming messages that don't
begin with these two frames.

* Behavior change: When a REQ socket gets an invalid reply, it used to
  discard the message and return EAGAIN. REQ sockets still discard
  invalid messages, but keep looking at the next one automatically
  until a good one is found or there are no more messages.
* Add test_req_request_ids.

- designed for TCP clients and servers
- added HTTP client / server example in tests/test_stream.cpp
- same as ZMQ_ROUTER + ZMQ_ROUTER_RAW + ZMQ_ROUTER_MANDATORY
- includes b893ce set ZMQ_IDENTITY on outgoing connect
- deprecates ZMQ_ROUTER_RAW

- ZMQ_CURVE_PUBLICKEY for clients and servers
- ZMQ_CURVE_SECRETKEY for clients
- ZMQ_CURVE_SERVERKEY for clients
- ZMQ_CURVE_SERVER for servers
- added tools/curve_keygen.c as example
- updated man pages

- renamed to ZMQ_PROBE_ROUTER

implement it for DEALER tocket.
+documentation

Add ROUTER socket option to introduce self(send an empty message) to new peers, to allow ROUTER<->ROUTER auto-discovery problem.

Add ROUTER socket option to introduce self(send an empty message) to new peers, to allow ROUTER<->ROUTER auto-discovery problem.

* ZMQ_PLAIN_SERVER, ZMQ_PLAIN_USERNAME, ZMQ_PLAIN_PASSWORD options
* Man page changes to zmq_setsockopt and zmq_getsockopt
* Man pages for ZMQ_NULL, ZMQ_PLAIN, and ZMQ_CURVE
* Test program test_security