Review request for JDK-8011884 and JDK-8011885

[Hannes Wallnoefer]

Please review these two patches:

http://cr.openjdk.java.net/~hannesw/8011884/
http://cr.openjdk.java.net/~hannesw/8011885/

The second one switches to Joni as default Regexp engine for Nashorn. 
Joni is about twice as fast as java.util.regex in the Octane RegExp 
benchmark. It also gives us more flexibility for tweaking the engine for 
our needs as we go forward.

Thanks,
Hannes