Merge branch 'master' of https://github.com/j6t/git-gui

Merge branch 'master' of https://github.com/j6t/git-gui

* 'master' of https://github.com/j6t/git-gui:
  git-gui: sync Makefiles with git.git
  git-gui: fix error handling of Revert Changes command
  git-gui--askyesno (mingw): use Git for Windows' icon, if available
  git-gui--askyesno: allow overriding the window title
  git gui: set GIT_ASKPASS=git-gui--askpass if not set yet
  git-gui: provide question helper for retry fallback on Windows
  git-gui: simplify using nice(1)
  git-gui: simplify PATH de-duplication