In the libsvn_client diff logic, move a few more output calculations up
the call chain from deep inside the diff calculations.

Eventually this code belongs in the diff writer, but small steps ahead..

* subversion/libsvn_client/diff.c
  (diff_prepare_repos_repos): Remove output argument.
  (diff_repos_repos): Don't calculate unused path. Calculate anchor in the
    same way the output code should do it later.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1570257 13f79535-47bb-0310-9956-ffa450edef68