Shutdown drytek4 SNF 2006-08-08 09:52:54: Tuning fix only works for SF6 (i.e. for low voltages)

[jimkruger at snf.stanford.edu]

Only SF6 can be tuned by the "semi-automatic" procedure.  Other gases (O2 or CHF3-O2) with higher voltages give high reflected and "flickering" plasma.