Switch to three-way text-conflict markers for merge and update.

* subversion/libsvn_wc/merge.c
  (do_text_merge): Choose three-way text-conflict marker.

* subversion/bindings/swig/ruby/test/test_client.rb
  (test_resolve_merged): Expect new output.

* subversion/tests/cmdline/basic_tests.py
  (basic_conflict, automatic_conflict_resolution): Expect new output.

* subversion/tests/cmdline/checkout_tests.py
  (co_with_obstructing_local_adds): Expect new output.

* subversion/tests/cmdline/merge_tests.py
  (textual_merges_galore): Pass extra revision.
  (merge_conflict_markers_matching_eol,
   merge_automatic_conflict_resolution,
   conflict_naming): Expect new output.

* subversion/tests/cmdline/trans_tests.py
  (update_modified_with_translation): Expect new output.

* subversion/tests/cmdline/update_tests.py
  (update_to_resolve_text_conflicts, conflict_markers_matching_eol,
   update_with_obstructing_additions, update_conflicted,
   update_accept_conflicts): Expect new output.

* subversion/tests/cmdline/svntest/actions.py
  (inject_conflict_into_expected_state,
   inject_conflict_into_expected_state): Add revision parameter.
  (make_conflict_marker_text): Generate three-way marker.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1591951 13f79535-47bb-0310-9956-ffa450edef68