PLOT_LCUR is a low level generic plotting routine used by several other routines.
The routine returns the list of subscripts which are between the times selected
by the user. The user clicks on the plot with the left button to define a new start time,
the right button to define an end time, and the middle button to exit. The user can
expand a time range after marking the start/stop times by clicking with the left
button on the box in the lower right corner. Some of the more simple calls are:
IDL> ss = plot_lcur(roadmap, gt_sxs1(roadmap))
IDL> ss = plot_lcur(index, gt_sum_l(index), plotr=a, title=title)
IDL> ss = plot_lcur(index, gt_sum_l(index), /nohard)