Add test for attempts to export a nonexistent URL.
Add test for attempts to export a nonexistent URL.

* subversion/tests/cmdline/export_tests.py
  (export_nonexistent_url): Add test which verifies that attempts to
   export a nonexistent URL produce an error.
  (test_list): Add export_nonexistent_url() to the list.

Patch by: mf
(Tweaked by me.)

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