[plexil-support] Default script file

[Reid S. <re...@cs...>]

run-ue plans/site-survey.plx
Running UE from /usr0/reids/code/plexil/universal-exec
  Plan:      plans/site-survey.plx
  Script:    
/usr0/reids/code/plexil/universal-exec/Exec/test/scripts/empty-script.pls
  Libraries:

Note that the script is, in fact, called empty-script.plx.  Not sure 
where the default name is kept, but it probably should be changed.

Reid