Wrote a GIMP extension to do scaling, EXACTLY what I want

This extension provides four functions for changing image size: 

1) Decrease size by 15%: ","
2) Increase size by 15%: "."
3) Decrease size 2x:     "Alt-,"
4) Increase size 2x:     "Alt-."

Then I defined four keyboard shortcuts mentioned in quotes above and
now I have the EXACT functions that I had in xv. 

I am a very happy GIMP user now, because I know that I can automate
what I do in the way I want. I have no clue about Scheme, but I am a
computer programmer and I can do "intelligent cut and paste from
google".

Source code follows:
######################################################################
;; Image rescaling. Copyright (C) Igor Chudov, Licensed under GPL 2.0
(define (script-fu-rescale img
                           factor
                           )
  ;; rescale

  (gimp-image-scale img 
                    (* (car (gimp-image-width img)) factor)
                    (* (car (gimp-image-height img)) factor)
                    )
  ;; Flush the display
  (gimp-displays-flush)
)

(define (script-fu-rescale-up img) 
  (script-fu-rescale img 1.15)
)
(define (script-fu-rescale-down img) 
  (script-fu-rescale img 0.8695)
)

(define (script-fu-rescale-up2x img) 
  (script-fu-rescale img 2)
)
(define (script-fu-rescale-down2x img) 
  (script-fu-rescale img 0.5)
)

(script-fu-register "script-fu-rescale-up"
                    "Rescale Up 15%"
                    "Rescale Up 15%"
                    "Igor Chudov"
                    "Igor Chudov"
                    "2008"
                    "RGB*, GRAY*"
                    SF-IMAGE    "Image"         0
                    )
(script-fu-menu-register "script-fu-rescale-up"
                         "<Image>/Script-Fu/Rescale")

(script-fu-register "script-fu-rescale-down"
                    "Rescale Down 15%"
                    "Rescale Down 15%"
                    "Igor Chudov"
                    "Igor Chudov"
                    "2008"
                    "RGB*, GRAY*"
                    SF-IMAGE    "Image"         0
                    )
(script-fu-menu-register "script-fu-rescale-down"
                         "<Image>/Script-Fu/Rescale")

;;;;;;;;;;;;;;;;;;;;;;;;;;;

(script-fu-register "script-fu-rescale-up2x"
                    "Rescale Up 2X"
                    "Rescale Up 2X"
                    "Igor Chudov"
                    "Igor Chudov"
                    "2008"
                    "RGB*, GRAY*"
                    SF-IMAGE    "Image"         0
                    )
(script-fu-menu-register "script-fu-rescale-up2x"
                         "<Image>/Script-Fu/Rescale")

(script-fu-register "script-fu-rescale-down2x"
                    "Rescale Down 2X"
                    "Rescale Down 2X"
                    "Igor Chudov"
                    "Igor Chudov"
                    "2008"
                    "RGB*, GRAY*"
                    SF-IMAGE    "Image"         0
                    )
(script-fu-menu-register "script-fu-rescale-down2x"
                         "<Image>/Script-Fu/Rescale")

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