0.3.41 let zit merge-tree --commit record a clean merge, but only when the
two sides had changed at least one file in common. The commonest clean
merge, a branch that touched different files from trunk, was refused with
"cannot scope the working area" and nothing was written.
0.3.42 records it. A forge can now merge any clean pair from the web with
zit merge-tree -R REPO FEAT --into trunk --commit -m MESSAGE --user NAME \
--expect-current TRUNK_TIP --expect-other FEAT_TIP
and get the check-in zit merge FEAT and zit commit would make in a
checkout. Nothing else changed.