Make the recording of mergeinfo use its own bookkeeping, instead of the
global path change state in the merge baton.

* subversion/libsvn_client/merge.c
  (prepare_merge_props_changed): Also check mergeinfo adds and removes in dry
    run mode.
  (remove_children_with_deleted_mergeinfo): Enable this function for dry run
    mode, to keep the child with mergeinfo list the same in both runs.
  (flag_subtrees_needing_mergeinfo): Add assertion. Verify that the child
    didn't have its mergeinfo removed.
  (record_mergeinfo_for_dir_merge): Add assertion.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1443020 13f79535-47bb-0310-9956-ffa450edef68