Now that we persist the labels, we can consistently use the labels in
prompts for the user without risk of confusion. This changes a huge amount
of command output:
This means that merge prompts like:
no tool found to merge a
keep (l)ocal, take (o)ther, or leave (u)nresolved? u
and
remote changed a which local deleted
use (c)hanged version, leave (d)eleted, or leave (u)nresolved? c
become:
no tool found to merge a
keep (l)ocal [working copy], take (o)ther [destination], or leave (u)nresolved? u
and
remote [source] changed a which local [dest] deleted
use (c)hanged version, leave (d)eleted, or leave (u)nresolved? c
where "working copy" and "destination" were supplied by the command that
requested the merge as labels for conflict markers, and thus should be
human-friendly.
