Rewrite event processing in io_thread

Code cleanup

Reverting fix for #393

Fixed issue #393 - Android build error

Fixed HWM doc on ZMQ_PULL

Making Android&pyzmq friendly version with -avoid-version

mtrie clenaup

Let docs for zmq_ctx_set_monitor() respect a 80 char wide column width

Small code simplification

Fix a bug in trie implementation

When removing keys for a specified value, make sure we drop
empty node table. Failing to do this can lead to asserion failure.

Refs: http://lists.zeromq.org/pipermail/zeromq-dev/2012-June/017589.html

declare struct iovec

avoids warnings of the form:

warning: 'struct iovec' declared inside parameter list
warning: its scope is only this definition or declaration, which is probably not what you want

when building downstream projects

Fix missing ENETRESET for Jira #LIBZMQ-329.

Missing semi-colon makes Windows compilation fail, Missing files in WIndows solution file

Add errno fallback values for MSVC2008.

Reworked ZMQ_FAIL_UNROUTABLE to actually work as it was intended.

Fix open_socket to return -1 (INVALID_SOCKET on Windows) on error

Connecter cleanups

Calling close () when the underlying socket is invalid
triggers an assertion failure.

Make start_connecting () to have singe exit point.