pipehistory()

- pipehistory() is a new definition/function callable from within the
individual tasks submenu (option 0) that lists the 'RUPIPE' and
'RUIMGTYP' header keywords for each image in the directory. Useful to
see what pipeline processes have been run on each image. Also explains
what each abbreviation in the string 'RUPIPE' means (e.g.,
'r'=specrectified, 'f'=flat-fielded, etc.).