Review request for JDK-8021350: Share script classes between threads/globals within context

[Hannes Wallnoefer]

Please review JDK-8021350: Share script classes between threads/globals 
within context:

http://cr.openjdk.java.net/~hannesw/8021350/webrev.01/
This makes script classes reusable by using appropriate guards and/or 
using dynamic parameter lookups instead of static bindings. Overall 
performance should roughly be the same. Applications that load the same 
script repeatedly will significantly benefit from this change, for 
example ant test262parallel runs more than twice as fast.

Thanks,
Hannes