Added support for System>>#fullGC

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Added primitive Integer class>>#fromString:

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Updated core-lib to match latest VM changes

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Added SystemTest to som_test.py as well.

Signed-off-by: Stefan Marr <git@stefan-marr.de>