The intent of this class is to provide a single entry/exit
point for the debug functionality contained in the S-PLUS
engine and accessed via the java connection.
The inner class LookupThread represents a separate thread to call
Naming.lookup the first time it needs to be called (namely to
find the SplusSessionFactory).
This is the 3rd version of SwingWorker (also known as
SwingWorker 3), an abstract class that you subclass to
perform GUI-related work in a dedicated thread.