move several query.c helper functions to client.c and rename

move several query.c helper functions to client.c and rename

- these formerly static helper functions have been moved into client.c
  and made external so that they can be used in hook modules as well as
  internally in libns: query_newrdataset, query_putrdataset,
  query_newnamebuf, query_newname, query_getnamebuf, query_keepname,
  query_releasename, query_newdbversion, query_findversion
- made query_recurse() and query_done() into public functions
  ns_query_recurse() and ns_query_done() so they can be called from
  modules.