Revision 165648

Fixes CONTINUUM-60: checkout in background
o The background check outs are implemented with a CheckOutProjectTask and
  COPTExecutor reading from the check out TaskQueue.
o Adding two more states: "checking out" and "updating".
o Adding a "project state guard" that's consulted by the ContinuumStore to
  ensure that the project is in a legal state at all times. This might not be
  the ideal solution to this problem but it's good enough for now.
o Updated some test to use the utility methods from
  ModelloJPoxContinuumStoreTest to create projects it's a bit more complicated
  now with the extra state transitions required to create a "new" project.
o Updating the integration tests as the tests have to wait for the check out to
  complete before continuing.
o Cleaned up the exception handling in Continuum a bit, making all exception
  instanciation go through a method to be able to centralize all logging. This
  implies that the core will log every exception it throws.
o Removed all logging from the ContinuumXmlRpc interface as the core does it
  now. The XML RPC clients will still get any exceptions returned as before.