smurf: Report an error if the telescope base position is bad in sc2ast
smurf: For PSSW acsis data replace bad jiggle positions with zero.
smurf: If telescope position is bad, skip the time slice rather than reporting an error

This allows a map to be made from an observation that contains a few bad values but is otherwise good.
smurf: Better gap filling

Because of the size of the fitting box, the old scheme could not handle
lots of small sections (less than 50 samples) of good and bad values next
to each other. The new scheme uses several passes. The first pass is just
like it used tobe. If the first pass leaves any unfilled gapos, then a
second pass is performed with a smaller fitting box (25 samples). If this
leaves any unfilled gaps a third pass is performed with an even smaller
fitting box (12 samples). If this leaves any gaps, an error is reported.

This issue cropped up making a map from FTS-2 data. The symptom was an
error in kpg1Fit1D.
smurf: End AST context correctly.