Ctrl-up and down now skipes 10 slices at a time.  Refactored code slightly.
Ctrl-up and down now skipes 10 slices at a time.  Refactored code
slightly.

ivoflipse/devide,fvpolpeta/devide,zhangfangyan/devide,zhangfangyan/devide,nagyistoce/devide,ivoflipse/devide,chrisidefix/devide,fvpolpeta/devide,chrisidefix/devide,nagyistoce/devide