Avoid performance regression in 'svn log' vs 1.7 when only passing a single
revision range. This regression was even bigger when running against a pre
1.5 server that doesn't implement svn_ra_get_location_segments().

In this case we run log against the youngest revision, which we already
resolved when opening the ra session.

* subversion/libsvn_client/log.c
  (svn_client_log6): Also apply the repository root optimization when we only
    have a single revision range as in this case we already resolved the path.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1553101 13f79535-47bb-0310-9956-ffa450edef68