Re: [PATCH 4/7] merge-ort: capture and print ll-merge warnings in our preferred fashion

> From: Elijah Newren <newren@gmail.com>
> 
> Instead of immediately printing ll-merge warnings to stderr, we save
> them in our output strbuf.  Besides allowing us to move these warnings
> to a special file for --remerge-diff, this has two other benefits for
> regular merges done by merge-ort:
> 
>   * The deferral of messages ensures we can print all messages about
>     any given path together (merge-recursive was known to sometimes
>     intersperse messages about other paths, particularly when renames
>     were involved).
> 
>   * The deferral of messages means we can avoid printing spurious
>     conflict messages when we just end up aborting due to local user
>     modifications in the way.  (In contrast to merge-recursive.c which
>     prematurely checks for local modifications in the way via
>     unpack_trees() and gets the check wrong both in terms of false
>     positives and false negatives relative to renames, merge-ort does
>     not perform the local modifications in the way check until the
>     checkout() step after the full merge has been computed.)