by the web server forks a child to do the actual work of calling tbend
and other stuff. The parent returns right away and the script ends.
When the experiment termination (child) ends, an email message is sent
to the user that issued the termination request. To prevent multiple
clicks, I added a DB field called expt_terminating that is a DATETIME
field.  If the field is set, the script fails and the user is told to
be more patient. I used a DATETIME field mostly for debugging purposes
so we can track and future problems.