Re: [PATCH/RFC] read-tree -m -u: do not overwrite or remove untracked working tree files.

>   This is an RFC patch that I consider of somewhat dubious value.
>   Not the implementation quality, but the semantic change it
>   implies.  Before, we could freely work in a working tree, which
>   is just a scratch area to build the index, littered with
>   throw-away files, knowing they would not prevent merge between
>   our HEAD and other branch from happenning even if a merge needs
>   to blow them away.  With this change, it is not a case anymore.
>   Your merge will fail to proceed and you have to remove those
>   throw-away files yourself and retry the merge.  The extent of
>   the damage can be seen by the change to t1002 test this commit
>   contains.  It arguably is making things much safer by refusing to
>   proceed, so this might be a desirable change.  I am still
>   undecided.