Katcp

* Add utility code to katcp.version.py that other modules can use to parse svn
or git revisions for use in build-state informs or sensors
* Add katcp.client.request_check: a convenience function for making KATCP
requests and raising an exception if there is an error.
* Add katcp.testutils.handle_mock_req() to allow mocked testing of server request
handlers and dispatch, removing the need to start() a DeviceServer for
handler tests.
* Make katcp.testutils.WaitingMock robust against race conditions
* Explicitly list set of base KATCP requests in katcp.server.BASE_REQUESTS
* Make method-name to KATCP-name function available outside KATCP server
metaclass
* Improvements to logging (i.a. prevents issues when using SocketHandler)
* Docstring cleanups

* Change event-rate strategy to always send an update if the sensor has
changed and shortest-period has passed
* Add differential-rate strategy

* Add convert_seconds() method to katcp client classes that converts
seconds into the device timestamp format.

* Fix memory leak in sample reactor when replacing sensor strategies
* Minor error reporting improvements in sampling strategies
* Fix 2012 -> 2013 in changelog :)

* Minor code comment cleanups
* Minor documentation and docstring updates
* Fix twisted katcp server's on-connect inform messages to be consistent
with the selected katcp version
* Improve error messages when an invalid sensor sampling strategy is set
* Fix bug in event-rate sampling strategy where events were sent whenever a sensor
object is updated, even if the value is unchanged. Also fixes same
bug for the event sampling strategy, since it uses the event-rate
code for its implementation
* Work around potential CPU livelock when sending messages and the network
buffers are full by using timeouts. Problem will be properly solved when the
current networking code is replaced by twisted.
* Fixed some buggy logger calls
* Improve the handling of sensor removal from the sensor tree
* made server main event loop robust against disconnect race-conditions when
looking up the client connection object