Merge https://github.com/j6t/gitk

Merge https://github.com/j6t/gitk

* 'master' of https://github.com/j6t/gitk:
  gitk: offer "Copy commit ID to X11 selection" only on X11
  gitk: support auto-copy comit ID to primary clipboard
  gitk: prefs dialog: refine Auto-select UI
  gitk: UI text: change "SHA1 ID" to "Commit ID"
  gitk: add text wrapping preferences
  gitk: make headings of preferences bold
  gitk: check main window visibility before waiting for it to show
  gitk: sv.po: Update Swedish translation (323t)