Merge pull request #136 from josh/es6-promise

Switch to ES6 Polyfill
build and include promises as npm dependencies
traceur location
Merge pull request #137 from calvinmetcalf/test-dep

traceur location
build and include promises as npm dependencies
spec update
circular references support
new System.register tests passing
circular and rebinding test completion
traceur compatibility fixes
update loaded condition check (ES bug 2602)
invariant checking
remove invariant checks