In the python tests: move common code to a library file, to avoid having test
files depending on each other (which sometimes causes completely unexected
side effects).

* subversion/tests/cmdline/depth_tests.py
  (diff_in_depthy_wc): Update reference.

* subversion/tests/cmdline/diff_tests.py
  (imports): Add svntest.verify import.
  (is_absolute_url,
   make_diff_header,
   make_no_diff_deleted_header,
   make_git_diff_header,
   make_diff_prop_header,
   make_diff_prop_val,
   make_diff_prop_deleted,
   make_diff_prop_added,
   make_diff_prop_modified): Move to svntest/verify.py

* subversion/tests/cmdline/log_tests.py
  Update import.

* subversion/tests/cmdline/svntest/verify.py
  (is_absolute_url,
   make_diff_header,
   make_no_diff_deleted_header,
   make_git_diff_header,
   make_diff_prop_header,
   make_diff_prop_val,
   make_diff_prop_deleted,
   make_diff_prop_added,
   make_diff_prop_modified): Moved here from ../diff_tests.py.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1570654 13f79535-47bb-0310-9956-ffa450edef68