resolve #1292 ZMQ_IDENTITY_FD does not validate option_len

Remove int typedefs and use stdint.h for windows.

Implement a definitive cygwin target for libzmq.

Problem: incomplete definition of integer types

Firstly, only a few types are defined, leaving it hard for higher layers
to complete the set. Secondly, the code incorrectly tries to use ifndef
to avoid re-defining typedefs, which does not work in C.

Solution: define all types, unconditionally for all MSVC compilers.
Additionally, define ZMQ_DEFINED_STDINT that tells higher layers that we
already defined these integer types.

Fixed atomic API, which used 'bool'

Solution: increase settle time for bind/unbind tests

zmq_atomic_counter_dec returned a 'bool' value, yet this isn't
defined by standard, so causes compile errors in upstream code.

Solution: return an int that can be safely converted to bool if
needed by bindings.

Problem: need atomic reference counting in several projects

Solution: as libzmq already provides this across all platforms,
expose an atomic counter API. I've not wrapped atomic pointers,
though someone who needs this may want to do so.

Problem: very hard to debug security mechanism mismatch

E.g. when server is not configured, and client tries PLAIN security,
there is no hint of why this does not work.

Solution: add debugging output for this case. Note that the various
debugging outputs for security failures should probably be sent to
an inproc monitor of some kind.

Problem: zmq_epgm is duplicate of zmq_pgm

There is zero benefit to this, and some confusion due to the special
case nature of this man page.

Solution: delete the zmq_epgm man page.

Fix #1274

reject old ZMTP connections if auth enabled

use explicit ZMTP/1.0 anonymous greeting
rather than HTTP request that just happened to work

- add ws2tcpip.h
- alias close->closesocket
- increment port in sec_null test

checks mechanism != NULL, or NULL + non-empty zap_domain

auth mechanisms were only enabled when ZMTP handshake
is latest version, meaning that connections from old sockets
would skip authentication altogether

fails on all auth mechanisms

Manual and welcome documentation

remove debug printf in test_xpub_welcome_msg

Manual and welcome

Fix issue #1257

Fix test_filter_ipc for cleared supplementary groups

This should fix part of [https://github.com/zeromq/libzmq/issues/1129].

Problem: linger values other than -1 or 0 are unsafe

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);

Fix busy-polling when reaching the rate limit