backport.pl conflicts mode: improve the warning summary by adding the
logsummarysummary (sic) to it.

To this end, change the %ERRORS global hash's values interface.

* tools/dist/backport.pl
  (merge, handle_entry): Track %ERRORS interface change.
  (logsummarysummary): New helper, factored out from..
  (handle_entry): .. here.
  (warning_summary): Include the logsummarysummary in the errput..


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1507639 13f79535-47bb-0310-9956-ffa450edef68