Stop whining about invalid base revisions when users request difference-type information on r0 (which is a valid revision, but by definition carries no "changes").
Stop whining about invalid base revisions when users request
difference-type information on r0 (which is a valid revision, but by
definition carries no "changes").

* subversion/svnlook/main.c
  (get_base_rev): New helper function.
  (do_dirs_changed, do_changed, do_diff): Now use get_base_rev() to
    fetch the base revision.  If there's no base revision, exit without
    further action.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion