backport.pl interactive mode: improve logs display.

* tools/dist/backport.pl
  (handle_entry): When showing logs of a backport branch, show the trunk logs
    too, since 'Merged r42 from trunk, resolving conflicts' isn't particularly
    informative.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1508697 13f79535-47bb-0310-9956-ffa450edef68