Simplify. Do not call toString() on values that are already strings.

This is backport of r1633448 and followup to r1633452 (BZ 57105).

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc7.0.x/trunk@1634316 13f79535-47bb-0310-9956-ffa450edef68