FCPPluginClient.sendSynchronous(): JavaDoc why it throws
InterruptedException

- For a detailled explanation of what InterruptedException is for,
typically this article is cited:
http://www.ibm.com/developerworks/java/library/j-jtp05236/
- Document that it is a shutdown request which should be honored
- Add a FIXME to check whether fred does interrupt() all threads
automatically. If it does, we don't have to implement our own shutdown
mechanism.