8144979: Context.fromClass should catch exception from Class.getClassLoader call

[Sundararajan Athijegannathan]

Please review http://cr.openjdk.java.net/~sundar/8144979/ for 
https://bugs.openjdk.java.net/browse/JDK-8144979
This fix is already in jake/nashorn. See also: 
https://bugs.openjdk.java.net/browse/JDK-8144568

In addition, I've moved all dynalink samples to 
$nashorn/samples/dynalink directory and renamed the README.

Thanks,
-Sundar