Implement LogicalExpression.
Fix behavior of instanceof null.  Wrap non-interpeter exceptions with JSExceptions.
Correctly pass env to interp during Throw call.
Merge pull request #3 from omphalos/logical-operators

Implement LogicalExpression.
Correctly call callback after handling the rror in CPS REPL.
Remove unnecessary check for JSException (since JSException inherits from InterpreterException).
Merge pull request #4 from omphalos/instanceof-fix

`instanceof null` fix
Add comment about short-circuiting bug.
Miscellaneous cleanup.

We don't need to check the type of the exception -- all InterpreterExceptions
are passed via errCont, instead of actually being thrown.
Switch to esprima's harmony branch.

This paves the way for supporting stuff like `yield`.

Removed for-in initializer test because it is ES6-incompatible.

Also uncovered a bug in the no-initializer case (ironically).
Remove JSException, support ternary if, support typeof ... == 'undefined'.
Implement ES6 generators.
Implement yield*.
Implement for-of loop.