Following up on r1440442, convert merge_file_added() to the diff processor
framework. Simplify the non-foreign merge code a bit.

* subversion/libsvn_client/merge.c
  (merge_file_added): Implement svn_diff_tree_processor_t api. Process
    properties after we know that we are going to use them. Don't use 'base'
    for pristine.
  (ignore_file_added): New stub.
  (merge_callbacks): Use stub.
  (do_merge): Set merge_file_added in processor.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1440463 13f79535-47bb-0310-9956-ffa450edef68