Add MOVe support to FSX.  This is mainly duplicating changes from FSFS.

* subversion/libsvn_fs_x/changes.c
  (CHANGE_KIND_MOVE,
   CHANGE_KIND_MOVEREPLACE): pro forma declaration of the new change kinds

* subversion/libsvn_fs_x/low_level.c
  (ACTION_MOVE,
   ACTION_MOVEREPLACE): declare new change type strings
  (read_change,
   write_change_entry): write / parse the new change types

* subversion/libsvn_fs_x/transaction.c
  (replace_change):  factored out from ...
  (fold_change): ... this one; handle moves similar to adds
  (process_changes): handle move-replaces similar to replaces
  (write_final_changed_path_info): update move source revs to Rev-1;
                     make changed_paths an input parameter
  (check_for_duplicate_move_source,
   verify_moves): new move verification code
  (commit_body):  verify moves when finalizing the commit;
                  update function all

* subversion/libsvn_fs_x/tree.c
  (enum copy_type_t): declare new parameter type
  (copy_helper): support moves just like ADDs; add extra param checks
  (x_copy,
   x_revision_link): update callers
  (x_move): add new function for MOVes


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1525429 13f79535-47bb-0310-9956-ffa450edef68