On the 'move-tracking-2' branch: Tweak, completing r1708952.
On the 'move-tracking-2' branch: Tweak, completing r1708952.

* subversion/libsvn_repos/ra_loader.c
  (svn_branch_get_mutable_state): Use svn_branch_revision_root_get_branches()
    instead of direct access.

git-svn-id: 486ec3464084f62cfe8608152673c827b947faa2@1708954 13f79535-47bb-0310-9956-ffa450edef68

YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion