add initial set of tests for Promise

For review, here are the first few tests for Promise 

These tests are based on the promises-es6 project, but have been converted from node/mocha to Test262 conventions.

I would be grateful for review and comments by the usual suspects (@anba, @bterlson, @getify, @domenic)

These tests mostly pass on current node v0.11.14.  "Mostly" because:

**THIS WAS A MISTAKE ON MY PART, FIXED BELOW**
1. v8 does not pass undefined as 'this' even though the spec requires this (regardless of strict/sloppy mode)

````
FAIL test/suite/es6/ch25/25.4/25.4.2/25.4.2.1/S25.4.2.1_A3.1_T1.js
     Promise.onFulfilled gets undefined as 'this'
     Exp: no error
     Got: 'this' must be undefined in onResolved (regardles of strict status), got [object global]

FAIL test/suite/es6/ch25/25.4/25.4.2/25.4.2.1/S25.4.2.1_A3.2_T1.js
     Promise.onRejected gets undefined as 'this'
     Exp: no error
     Got: 'this' must be undefined in onRejected (regardles of strict status), got [object global]

FAIL test/suite/es6/ch25/25.4/25.4.3/25.4.3.1/S25.4.3.1_A5.1_T1.js
     Promise executor gets undefined as 'this'
     Exp: no error
     Got: 'this' must be undefined in executor (regardless of strict status), got [object global]
````

2. v8 does not seem to handle foreign thenables correctly, or else I wrote the test wrong
````
FAIL test/suite/es6/ch25/25.4/25.4.4/25.4.4.5/S25.4.4.5_A3.1_T1.js
     Promise.resolve passes through an unsettled promise w/ same Constructor
     Exp: no error
     Got: Test262 Error: Test did not run to completion ($DONE not called)

FAIL test/suite/es6/ch25/25.4/25.4.4/25.4.4.5/S25.4.4.5_A3.1_T1.js
     Promise.resolve passes through an unsettled promise w/ same Constructor (Strict Mode)
     Exp: no error
     Got: Test262 Error: Test did not run to completion ($DONE not called)
````
I don't see any non-objects here.

In fact, the exception ("abrupt completion") you throw should be the rejection reason; it is captured and propagated to IfAbruptRejectPromise. The only reason you have a TypeError is because the incorrect Symbol usage.