Make the interactive conflict resolver code more table-driven: the responses
that simply choose a return value now get it from the table. Make the 'help'
response uniformly available with all four types of conflicts.

* subversion/svn/conflict-callbacks.c
  (resolver_option_t): Add a 'choice' field.
  (text_conflict_options, prop_conflict_options,
   obstructed_add_options, tree_conflict_options): Add the simple responses
    in the new column.
  (prompt_user): New function.
  (handle_text_conflict, handle_prop_conflict,
   handle_tree_conflict, handle_obstructed_add): Factor out the prompting
    and choosing of simple responses.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1440411 13f79535-47bb-0310-9956-ffa450edef68