SHOW SPECTRA Clean|Dirty|Sky|ImageVar
Display individual spectra in a Map-like display (one per box, placed at
their respective positions) from a 3-D SIC variable, assumed to be in
the LMV order.
Note: the second argument may be omitted to re-display the same dataset
with different control parameters. SHOW SPECTRA is however not fully
protected against changes in the data set between two invocations, so
this should only be used for consecutive commands.