Re: [PATCH] checkout -f: do not leave untracked working tree files.

> Earlier we did not consider untracked working tree files
> "precious", but we have always considered them fair game to
> clobber.  These days, branch switching by read-tree is more
> careful and tries to protect untracked working tree files.  This
> caused the following workflow to stop working:
>
> 	git checkout one-branch-with-file-F
> 	git checkout -f another-without-file-F
> 	git pull . one-branch-with-file-F
>
> Because the second checkout leaves F from the previous state as
> untracked file in the working tree, the merge would fail, trying
> to protect F from being clobbered.
>
> This changes "git checkout -f" to remove working tree files that
> are known to git in the switched-from state but do not exist in
> the switched-to state, borrowing the same logic from "reset --hard".
>