Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

Threads were so far identified by integers called 'slots'.
This patch renames them to more comprehensible 'tid's (thread IDs).
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

    1. ZMQ_LINGER option can be set/get
    2. options are part of own_t base class rather than being declared
       separately by individual objects
    3. Linger option is propagated with "term" command so that the
       newest value of it is used rather than the stored old one.
    4. Session sets the linger timer if needed and terminates
       as soon as it expires.
    5. Corresponding documentation updated.
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

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.

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.

This commit introduces the necessary changes necessary
for implementing flow control. None of the socket types
implements the flow control yet. The code will crash when
the flow control is enabled and the thw lwm is reached.

The following commits will add flow-control support for
individual socket types.

zmq_encoder/decoder are able to add/trim prefixes from messages; fair queueing and load balancing algorithms factorised into separate classes

This reverts commit 88695aae.