Factor out some common code in conflict handling.

* subversion/libsvn_wc/conflicts.c
  (merge_showing_conflicts): New function, factored out ...
  (eval_text_conflict_func_result,
   resolve_text_conflict_on_node): ... of these two functions.
    Also note that these two functions are redundantly similar.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1480670 13f79535-47bb-0310-9956-ffa450edef68