Locking problems with DorothyLocker

I started using the pyds version from cvs and noticed locking problems if I started 
pyds with the verbose option.

To track down the problems I changed Tool.py at two places:

* the tool threads are created with the tool name as thread name
* the lock object (DorothyRLock) are created with verbose=True

After these changes I noticed that DorothyRLock did not always lock correctly - it 
seemed to not block if a lock was already acquired by another thread. To correct 
this I changed the second locking attempt to _RLock.acquire(self, blocking=1)

This change removed most of the locking problems, however sometimes I had an 
error message about prevcontext not being initialized. So I also added some code 
to always initialize prevcontext to None.

Garth, as you have written DorothyLocker, could you please review these patches 
and submit them to Georg?

Regards,

Thomas