wls =
MakeItWls(S)
If argument is a [start delta n] description or
a struct with fields start, step, numberSamples,
it is expanded to an actual list of wavelengths.
A passed list of wavelengths is left alone.
7/27/02 dhb Handle struct format too by calling
MakeItS first.
Psychtoolbox/PsychColorimetric/MakeItWls.m