Major flaw! RS232 is single resource shared by all clients.  Hence each
RS232 read/write has to be locked to each client.  Needs some thought.
Changed to subclass actionclass from Pyro.core.SynchronizeObjBase. This
means all method calls are synchronised by putting a thread lock object
on the pyro object, ie all method calls are serialialised hence the
serial port will be used by one and one only method call at a time.