Review request for JDK-8051889: Implement block scoping in symbol assignment and scope computation

[Hannes Wallnoefer]

Please review JDK-8051889: Implement block scoping in symbol assignment 
and scope computation:

http://cr.openjdk.java.net/~hannesw/8051889/webrev.04/

This is an rather complete implementation of lexical scoping as defined 
in ES6. Still missing is some special treatment of for-let loops and 
switch statements.

Thanks,
Hannes