Add test for issues #3589, #4000
Add test for issues #3589, #4000

* subversion/tests/cmdline/externals_tests.py
  (copy_file_externals): New test.

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