Merge git://ozlabs.org/~paulus/gitk

* git://ozlabs.org/~paulus/gitk:
  gitk: On OSX, bring the gitk window to front
  gitk: Add support for -G'regex' pickaxe variant
  gitk: Add menu item for reverting commits
  gitk: Simplify file filtering
  gitk: Display the date of a tag in a human-friendly way
  gitk: Improve behaviour of drop-down lists
  gitk: Move hard-coded colors to .gitk