Enable custom keywords when patching.

* subversion/libsvn_client/patch.c
  (obtain_eol_and_keywords_for_file): Use svn_subst_build_keywords3.

* subversion/tests/cmdline/patch_tests.py
  (patch_with_custom_keywords): New test.
  (test_list): Add new test.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1466823 13f79535-47bb-0310-9956-ffa450edef68