Review request for JDK-8057980: let & const: remaining issues with lexical scoping

[Hannes Wallnoefer]

Please review JDK-8057980: let & const: remaining issues with lexical 
scoping:

http://cr.openjdk.java.net/~hannesw/8057980/

Summary of changes:
  - Throw error when let/const declaration is used in single-statement 
context as it is not a statement
  - Implement per-iteration scope in for(let ; ;) loop
  - Throw error for let/const in top-level switch statement. This should 
be supported, but we can't implement this correctly without a bigger 
rewrite of switch statement handling.
  - Overwriting const binding from different script should throw type 
error also in non-strict mode.
  - Removed unused flags: VarNode.IS_STATEMENT and ForNode.IS_FOR

Thanks,
Hannes