do not assume the current branch is the most recent
do not assume the current branch is the most recent

Look through the other branches to find the previous branch and
determine where to stop scanning, instead of assuming the current branch
is the most recent and trying to artificially compute the previous
branch.

Change-Id: If905575a47c828ebe43e79a6c0f363eaa3226f6e
Signed-off-by: Doug Hellmann <0798ebecfb7bc4dfb9d0445c2fa030eb64e1fa1c@doughellmann.com>

openstack/reno