Improve ExprTransformConstantFold to not unecessarily call copySubstitute on non-foldable expressions (JENA-630)

git-svn-id: https://svn.apache.org/repos/asf/jena/trunk@1586211 13f79535-47bb-0310-9956-ffa450edef68
Further test from Andy around non-foldable expressions (JENA-630)

git-svn-id: https://svn.apache.org/repos/asf/jena/trunk@1586212 13f79535-47bb-0310-9956-ffa450edef68