Rewrite the select()-based zmq_poll() implementation to use
ZMQ_FD and ZMQ_EVENTS.

Also fix some corner cases: We should not pollute revents with
unrequested events, and we don't need to poll on ZMQ_FD at all
if a pollitem with no events set was passed in.

Dunno where those <TAB>s came from...

Rewrite zmq_poll() to use ZMQ_FD and ZMQ_EVENTS introduced on the
wip-shutdown branch. Only do the poll()-based version of zmq_poll (), the
select()-based version will not compile at the moment.

Sockets may now be migrated between OS threads; sockets may not be used by
more than one thread at any time. To migrate a socket to another thread the
caller must ensure that a full memory barrier is called before using the
socket from the target thread.

The new zmq_close() semantics implement the behaviour discussed at:

http://lists.zeromq.org/pipermail/zeromq-dev/2010-July/004244.html

Specifically, zmq_close() is now deterministic and while it still returns
immediately, it does not discard any data that may still be queued for
sending. Further, zmq_term() will now block until all outstanding data has
been sent.

TODO: Many bugs have been introduced, needs testing. Further, SO_LINGER or
an equivalent mechanism (possibly a configurable timeout to zmq_term())
needs to be implemented.

Add some basic documentation for XREQ/XREP socket types, including
a brief description of the most common use case (REQ -> XREP) and (XREQ ->
REP).

Function returning unsigned long int cannot return (-1)

http://github.com/zeromq/zeromq2/issues#issue/46
Invalid messages are now discarded silently, instead of causing an assertion
failure.

* Fixed zmq_term, zmq_socket, zmq_close, zmq_setsockopt,
* zmq_getsockopt, zmq_bind, zmq_connect, zmq_send,
* zmq_recv, zmq_poll, zmq_device, zmq_stopwatch_stop
* Updated Reference Manual for these methods

* zmq_term
* zmq_socket
* zmq_close
* zmq_setsockopt
* zmq_getsockopt
* zmq_bind
* zmq_connect
* zmq_send
* zmq_recv
* zmq_poll
* zmq_device
* zmq_stopwatch_stop

This patch restarts the send() or recv() inside zmq::signaler_t if the call fails
due to EINTR.

* Clarified broker model and proxy model
* Added example of proxy model

- fixed unwrapped text in new man pages
- fixed over-long lines in older pages, where possible
- removed reference to old standalong devices from index page
- added refernce to new zmq_device[3] documented from index page
- some minor spelling corrections

* Added documentation for zmq_deviced, which we're developing
* Created consistent page footer in documentation template
* Page footer notes doc authors and copyright statement

definitions as aliases, to be removed in release 3.0.  Also renamed the source
files implementing these two socket types.  This change does not break existing
applications nor bindings, but allows us to fix the documentation and user guide
now, rather than keeping the old (confusing) names.