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)
````
Oh I see what you're doing now. I don't think this approach works too well though. An implementation that gets expectedThis wrong will pass even though the promises are not behaving to spec. You can be explicit with separate tests for strict and non-strict mode (using the onlyStrict and noStrict flags).