Fix 10 - make pymca process from a thread

Some work on processing: using multiprocessing.pool, thread for gui computation...

for now thread computation will be very raw, we will launch processing in a thread, if new computation is requested then the current thread is stopped, released and a new thread is requested. No 'processing stack' is excepted.

some small / short benchmark made for threading.pooltest.py

/close #10 (closed)