Merge branch 'js/ask-yesno'

* js/ask-yesno:
  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

Signed-off-by: Johannes Sixt <j6t@kdbg.org>