ISPN-3242 Enforce building against JDK7

ISPN-3242 Enforce building against JDK7 but verify that we are compatible with JDK6. Run testsuite against JDK6 if the JAVA_HOME_16 environment variable is set

ISPN-3284 Drop useless dependencies which we had to keep around because of http://bugs.sun.com/view_bug.do?bug_id=6550655

Other minor pom cleanups

https://issues.jboss.org/browse/ISPN-3242
https://issues.jboss.org/browse/ISPN-3284