Fix the copy-from revision number reported in a diff header. It previously
reported 'nonexistent' instead of the copy-from revision in some cases.

This bug seems to be a regression; 1.8.x releases show the correct revision.

* subversion/libsvn_client/diff.c
  (diff_file_added, diff_dir_added): Pass on the copy-from revision number.

* subversion/tests/cmdline/diff_tests.py
  (diff_git_format_wc_wc,
   diff_local_copied_dir): Update the expected output.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1619452 13f79535-47bb-0310-9956-ffa450edef68