[PATCH] Use os.path.join in copy_tests.py

Found these while crawling through the tests.

-Hyrum

[[[
Use os.path.join() in the tests instead of hardcoding specific path
separators.

* subversion/tests/cmdline/copy_tests.py
  (resurrect_deleted_dir, copy_deleted_dir_into_prefix,
  copy_modify_commit, copy_delete_commit, mv_and_revert_directory):
  Don't concatenate paths manually, use os.path.join() instead.
]]]