Following up to r1545081: clean up the mergeinfo normalization checking code.

* subversion/libsvn_repos/dump.c
  (check_mergeinfo_normalization_baton, check_mergeinfo_normalization):
   New hash iterator function and baton.
  (dump_node) Move mergeinfo normalization checks to the
   check_mergeinfo_normalization hash iteratino function.
  (check_name_collision_baton): Renamed from check_name_baton.
  (check_name_collision, verify_close_directory): Update uses of
   check_name_collision_baton.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1545149 13f79535-47bb-0310-9956-ffa450edef68