SearchVESA()

         Searches the VESA mode of a gif file

    Syntax:

         SearchVESA ( cFile ) -> nMode

         cFile : Name of the GIF file

    Description:

         Initializes a GIF file and returns the appropriate VESA mode to
         display the image.

    Return:

         The appropriate VESA mode or Nil if cFile not exist, cFile is not
         a GIF file or the size of GIF file is unknown.

    Example:

         cFile    := "f:\xxx\car.gif"           // 1024x768x256
         ? SearchVESA( cFile )                  // VESA mode 261