Make SVNTreeUnequal failures easier to trace in regression tests, byadding a label to the tree (e.g., "output", "disk", "status", etc).This change is not really as large as it looks: the bulk of it is justfallout from removing some unused parameters to run_and_verify_commit,which is really a separate change, but which is also intertwingled invarious ways with the label/singleton changes.* subversion/tests/cmdline/svntest/tree.py (compare_trees): Take a new label parameter, use it to construct the compare_trees.display_nodes() inner function and the singleton handlers and batons. (default_singleton_handler): Replace default_singleton_handler_a and default_singleton_handler_b with this one function, and depend on the description parameter (formerly called baton) to distinguish the two sides. * subversion/tests/cmdline/svntest/actions.py (setup_pristine_repository, run_and_verify_unquiet_status, run_and_verify_status, run_and_verify_merge2, LogParser.extra_skip, run_and_verify_export, run_and_verify_checkout, run_and_verify_diff_summarize, verify_update): Pass new label arguments to tree.compare_trees(), and fix some doc strings along the way. (run_and_verify_commit): Same, and remove the singleton handler parameters, which were entirely unused. (inject_conflict_into_wc): Update call to run_and_verify_commit.* subversion/tests/cmdline/*: Adjust callers of run_and_verify_commit() and compare_trees() for above changes.