Thread handling issue

[Paul]

Basically there can be quite a big job to do based on the user selection and
I've pipelined it so after the user selects the output location the next job can 
get started so long as the first job (preparing the data) has been running for 5 
or so seconds roughly. Its just a lot nicer to have this done by the time the
user has selected an output folder so the main job can start instantly. Of course
the user can kill the main job too and go back to the user input so I need to be
able to kill the threads anyway.