With generate-working-copy-states.py generalized to support
arbitrarily many changesets, we can use it for generating test cases
for merge: use one changeset each for base, remote and local. With the
various working copy states, this is a total of 104 cases.
The first candidate for additional testing is 'hg merge --force'. Even
though the force option is deprecated, it is convenient for testing
because it can be tested without first needing to revert any
changes. Except for the lack of checking for uncommitted changes, it
differs in only a few cases from unforced merge.
The new tests cover all the cases in the existing test-merge-force.t,
except for the unforced merge case, which is covered in several other
files anyway, so nothing remains of the file after this patch.
Makes the 'nothing to merge' abort messages in commands.py consistent with
those in merge.py. Also makes commands.merge() and merge.update() use hints.
The tests show the changes.