Help for the Image Combine Widget

Images that are loaded into idp3 may be combined using the Image Combine
Widget (Combine Images entry in the Images Menu on the Main Display).
Only "ON" images may be combined.  Any alignment, rotation, scaling,
etc. are performed on the images before they are combined.  All masked
pixels are excluded from the combination.

Images may be mean or median combined.  Both mean and median combinations
may be sigma clipped.  Sigma clipping limits may be defined in the widget
or the default values from the idp3_preferences file may be used.

In addition to the combined data image there are 3 optional files that
may be produced:

    1. a 2-D standard deviation image which shows the RMS of each resultant
       pixel in the output image
    2. a 2-D number of pixels image that shows how many pixels contributed 
       to each of the output pixels
    3. a 3-D image representing the number of sigma each pixel in each
       input image deviates from the mean or median for that pixel.

Images 1 and 2 may be saved to idp3 memory and/or disk as a fits file.
Image 3 may only be saved to disk because of its dimensionality.

Name refers to the name given to the resultant image in the idp3 ShowImages
Widget (saving to memory) if IDP3 is selected and/or the name of the output
fits file it File is selected.  If no name is given no results are saved and
a warning message is given.  The default path for saving files to disk is
the current "savepath".

One may use the browse button to locate the proper output path.  Compute
computes the image combination, Help shows this file, and Done ends the
widget.