Pycsp

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* Changed retire() behaviour, to propagate a retire pill. Added ChannelRetireException.
* Fixed possible deadlock, when doing several concurrent alternations on an input
and output guard. This is an issue in pycsp.threads and pycsp.net.
- See examples/problems/deadlock_doing_alternation_on_input_and_output_pre_0.6.1.py
* Added a Pyro nameserver lookup to the PyroServerProcess thread, to avoid sharing
of a global Pyro nameserver proxy, which is not recommended by Pyro.
* Changed greenlet dependency to the greenlet 0.2 module available at http://pypi.python.org/pypi/greenlet
* Added new Channel methods for returning ChannelEnd objects. +C / -C and C.reader() / C.writer()

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* Added 3 new implementations of PyCSP
- Processes : Uses the multiprocessing module.
- Greenlets(coroutine) : Uses a third party py.magic.greenlet module from pylib.
- Net : Uses Pyro to enable all channels as remote channels.
* Modified examples and tests to support all 4 implementations (threads, processes,
greenlets, net)
* import pycsp, defaults to pycsp.threads
* Added a TestSuite system to doctest. Execute python __init__.py to run testsuites.

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* Added doctest items to classes and functions.
* Fixed Sequence(*plist) to accept list of processes.

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The PyCSP library has been completely rewritten.

There is no backwards compatibility.

For now please look at the examples for documentation on how to use the library.