Merge branch 'pt/git-gui' into maint

* pt/git-gui:
  git-gui: fix size and position of window panes on startup
  git-gui: mc cannot be used before msgcat has been loaded
  git-gui: use textconv filter for diff and blame
  git-gui: Avoid using the <<Copy>> binding as a menu accelerator on win32
  git-gui: fix shortcut creation on cygwin
  git-gui: fix PATH environment for mingw development environment
  git-gui: fix usage of _gitworktree when creating shortcut for windows
  git-gui: fix "Explore Working Copy" for Windows again
  git-gui: fix usage of themed widgets variable
  git-gui: Handle failure of core.worktree to identify the working directory.
  git-gui: check whether systems nice command works or disable it