On the 'move-tracking-2' branch: Minor refactoring.

* subversion/svnmover/svnmover.c
  (family_add_new_branch): Delete.
  (family_add_new_branch_definition,
   family_add_new_branch_instance): New.
  (branch_branch_subtree_r, svn_branch_branchify): Adjust callers.

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/move-tracking-2@1629202 13f79535-47bb-0310-9956-ffa450edef68