pull: fix shallow clone when lastest change isn't HEAD. Previously, using `hg clone --startrev HEAD` when the actual HEAD revision didn't touch the prefix, would cause it to report that no changes were found. Using last_changed_rev instead of HEAD fixes this. In order to better test this scenario, we now clone the trunk subdirectory of all the fixtures.

#!/bin/sh
. $(dirname $0)/common.sh

for b in `hg branches -aq` ; do
    hg co $b || break
    echo verifying $b
    hg svn verify
done