backport.pl: Avoid fragile use of global variable.  No functional change.

* tools/dist/backport.pl
  (parse_entry): Instead of using $., accept $parno from the caller.
  (handle_entry): Percolate it.
  (backport_main): Pass $. ($INPUT_LINE_NUMBER) to callee.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1570043 13f79535-47bb-0310-9956-ffa450edef68
backport.pl: Relax the vetoes parser.

* tools/dist/backport.pl
  (handle_entry): Allow an arbitrary amount of whitespace in front of vetoes.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1570044 13f79535-47bb-0310-9956-ffa450edef68