Added code in renumber.c and test in t.csetprune to handle case where a delta needs to have its parent and merge deltas swapped. This is because the trunk is determined by the oldest child of a multi child delta.  The prune can remove the oldest delta, and the new oldest delta is now on the branch. So renumber now not only puts the branch onto the trunk, but rewires the relation between merge and parent.
Added code in renumber.c and test in t.csetprune to handle case
where a delta needs to have its parent and merge deltas swapped.
This is because the trunk is determined by the oldest child of
a multi child delta.  The prune can remove the oldest delta, and
the new oldest delta is now on the branch.
So renumber now not only puts the branch onto the trunk, but rewires
the relation between merge and parent.

bk: 3af0b7aeFDfiKmyysReJCRwq5tux9A
bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper