#669 Cutting on stack call

https://github.com/junit-team/junit/issues/669#issuecomment-58889044

The class Packages represents the packages that must be filtered whe the stacktrace will be printed, an instance of packages are passed to the TraceFilter, that do the filtering...

- If the user just pass -filterstack argument, the stack will be filtered with some "default packages".
- If they pass -filterstack [pkg1, pkg2, pkg3] the pkg1,pkg2,pkg3 will be filtered from the trace. (-filterstack [java.lang, junit.framework, org.eclipse]) ....