Downgraded Guava to 13.0.1 because of issues with Java EE 7 containers

Downgraded Guava to 13.0.1 so that it's possible to deploy apps that use Kundera into Java EE 7 containers, such as Glassfish 4. See https://code.google.com/p/guava-libraries/issues/detail?id=1433

Signed-off-by: Paulo Pires <pjpires@gmail.com>