SEC-697: Add setOwner(Sid) to MutableAcl interface.

acl/src/main/java/org/springframework/security/acls/MutableAcl.java

@@ -56,6 +56,13 @@ public interface MutableAcl extends Acl {
     void insertAce(Serializable afterAceId, Permission permission, Sid sid, boolean granting)
         throws NotFoundException;
 
+    /**
+     * Changes the present owner to a different owner.
+     * 
+     * @param newOwner the new owner (mandatory; cannot be null)
+     */
+    void setOwner(Sid newOwner);
+
     /**
      * Change the value returned by {@link Acl#isEntriesInheriting()}.
      *