coyote: CGIMAGEGROUP__DEFINE

The initialization module for the cgImageGroup object creates a specific
instance of the object.
Keywords:filename: in, optional, type=string
   The name of an IDL image file that IDL can read with READ_IMAGE.
reverse: in, optional, type=boolean, default=0
   Set this keyword to reverse the image in the Y direction before display.
The class definition module for the cgImageGroup object.