This method returns TRUE if a point is within the old Image structure box
defined by the Image structure's LeftEdge, TopEdge, Width, and Height
fields.  Subclasses of imageclass can redefine this method if they need to
change the criteria for deciding if a point is within an image.
Application programs should not call this method directly, instead use the
Intuition function PointInImage().  The IM_HITTEST method uses a custom
message structure:

    struct impHitTest
    {
        ULONG MethodID; /* IM_HITTEST */
        struct
        {
            WORD X;     /* Coordinates of point to test for hit */
            WORD Y;
        } imp_Point;
    };

If an image object doesn't need to make any changes to how its superclass
handles IM_HITTEST, it can blindly pass this method on to its superclass.