To Do list for idl tgcmproc:

1. Teach it to read netcdf output files written by fortran tgcmproc.

2. It should be able to read a file in which the first var is
   only 3d (e.g., height-indep), e.g., Gang's fof2,hmf2 files
   from fortran tgcmproc, or secondary history file where first
   var is 2d magnetic.

3. Perimeter latitude slider should be reset when switching from
   geo to mag var, or vice versa. It will also have to be reset
   in case 2 above. Maybe a pro reset_perimlat_slider.

4. Plot Options: image, image+contour, or contour.

5. Allow user to spec lat0,lat1, lon0,lon1 for ce plots.

6. Allow user to spec min,max of field to plot

7. Derived fields.