FCPClientReferenceImplementation.FCPMessageHandler(): Consume original
FCPPluginMessage

...instead of passing its content SimpleFieldSet/Bucket. This is a
necessary change so FCPErrorHandler can be changed to read the errorCode
field of the FCPPluginMessage, which will happen in following commits.
AbstractJUnit3BaseTest: Remove deprecated doRandomChangesToWOT()

- The function has been copied to AbstractJUnit4BaseTest already, and
all callers already use that class instead of this one here.
AbstractJUnit4BaseTest.doRandomChangesToWOT(): Fix
IllegalArgumentException / infinite loop

- IllegalArgumentException: "n must be positive" Would haven if we did
RandomGrabHashSet.getRandom() while the set was empty
- Infinite loop in while(truster == trustee) would happen if the set
only contained 1 identity instead of at least 2.