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.
Merge pull request #577 from ControlSystemStudio/bug576

Fix Compiler errors when not using Oracle JDK