Merge branch 'jg/revert-untracked'

git-gui learned to delete untracked files when the "Revert Changes"
option is selected. Since there are two types of revert operations (one
for tracked files and one for untracked ones), the "checkout" and
"deletion" operations are done in parallel. The status bar is updated
to allow both to use it in parallel.

* jg/revert-untracked:
  git-gui: revert untracked files by deleting them
  git-gui: update status bar to track operations
  git-gui: consolidate naming conventions