Upgrade plugin dependencies to current versions.

Used `mvn versions:use-latest-versions` to update all the plugins to their current versions, both for Maven 3.1 compatibility and just to stay up-to-date.

Exceptions:
*  I left Jetty at 6.1.26 and did not upgrade to 7.0.0.pre5.
*  I migrated from `org.codehaus.groovy.maven:gmaven-plugin:1.0` to `org.codehaus.gmaven:gmaven-plugin:1.5`.  Notice the change in group ID.