Fix Compiler errors when not using Oracle JDK

A few sources depend on *.sun.* classes which are available in the
Oracle JDK but not necessarily in generic Java 5, 6 or 6.
When .classpath enforced plain JavaSE 5, 6, 7, those sources would not
compile.

Helps with #576 because sources compile again as long as one uses the Sun/Oracle JDK.
Complete fix would remove dependencies on *.sun.* classes