In the tree conflict tests, enable testing with an incoming file
replacement.  For 'switch', don't test with incoming replacements because
'switch' ignores ancestry in its repos diff (unlike 'update') and so does
not notice replacements.

Eliminate two helper functions, in the interest of clarity.

* subversion/tests/cmdline/tree_conflict_tests.py
  (f_rpls): Enable testing with an incoming file replacement.
  (ensure_tree_conflict): Make the 'commit_local_mods' parameter optional.
  (test_tc_up_sw, test_tc_merge): Delete.
  (...elsewhere...): Call ensure_tree_conflict() directly. Don't test
    'switch' with incoming replacements.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1449428 13f79535-47bb-0310-9956-ffa450edef68