Add a working copy query test to automatically find queries with an idential
query plan as not having duplicates reduces maintenance and helps avoiding
query planner costs.

* subversion/libsvn_wc/upgrade.c
  (migrate_single_tree_conflict_data): Use existing instead of specialized
    queries.

* subversion/libsvn_wc/wc-queries.sql
  (STMT_DELETE_MOVED_BACK): Remove duplicate.
  (STMT_UPDATE_ACTUAL_CONFLICT_DATA,
   STMT_INSERT_ACTUAL_CONFLICT_DATA): Remove duplicates.

* subversion/libsvn_wc/wc_db.c
  (handle_move_back): Update query user.

* subversion/tests/libsvn_wc/wc-queries-test.c
  (includes): Add svn_hash.h.
  (test_query_duplicates): New function.
  (test_funcs): Add test_query_duplicates.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1538962 13f79535-47bb-0310-9956-ffa450edef68