Review requests for JDK-8012931 and JDK-8008238

[Hannes Wallnoefer]

These are two trivial patches. JDK-8012931 has already been fixed by 
Marcus' and Attila's immutable IR patch, so this only contains a test:

http://cr.openjdk.java.net/~hannesw/8012931/
JDK-8008238 is a trivial patch to avoid NativeDate.safeToString() 
throwing a RangeError:

http://cr.openjdk.java.net/~hannesw/8008238/

thanks,
Hannes