Replace use of deprecated svn_ra_get_log2 in a couple of places.

* subversion/include/svn_ra.h (svn_ra_get_log2): Fix docstring.
* subversion/libsvn_client/merge.c (get_log): Use svn_ra_get_log3.
* subversion/libsvn_client/mergeinfo.c
  (logs_for_mergeinfo_rangelist): Likewise.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1534045 13f79535-47bb-0310-9956-ffa450edef68