In ra_serf optimize the obtaining of inherited properties for servers that
don't have the new in 1.8 report by pipelining the property requests. This
considerably speeds up update and checkout against high latency 1.8 servers
on paths deep in the repository.

* subversion/libsvn_ra_serf/inherited_props.c
  (includes): Add svn_sorts.h
  (iprop_rq_info_t): New struct.
  (keep_only_regular_props): New function.
  (get_iprops_via_more_requests): New function.
  (svn_ra_serf__get_inherited_props): Call get_iprops_via_more_requests when
    the repository doesn't report support for iprops.

* subversion/libsvn_ra_serf/ra_serf.h
  (svn_ra_serf__reparent): Add prototype.

* subversion/libsvn_ra_serf/serf.c
  (svn_ra_serf__reparent): Make library public.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1552475 13f79535-47bb-0310-9956-ffa450edef68