update: better logic and messages for updates - complain about attempts to merge with ancestor - when updating, differentiate between - crossing named branches with no local changes (jump) - crossing named branches with local changes (complain) - nonlinear update on the same named branch, no changes (complain some more) - nonlinear update on the same named branch, changes (different complaining)

adding a
marked working directory as branch b
adding b
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
fast-forward
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
bogus fast-forward should fail
abort: can't merge with ancestor
done