[JSB] Support Box2d with SpiderMonkey's asm.js

[pandamicro]

Result shown in this page: http://www.j15r.com/blog/2013/07/05/Box2d_Addendum indicate the performance of Box2d in asm.js is way faster than web.

It's probably sufficient for JSB, in this way, we no longer need bindings for Box2d

[zhaijialong]

👍

[IcePower]

火钳刘明！

[pandamicro]

A supplementary link to the test cases source:
https://github.com/joelgwebber/bench2d

	ms/frame	5th %ile	95th %ile	Ratio to C
C (clang-500.2.79)	2.14	1.89	2.41	1.00
pNaCl	2.61	2.31	2.92	1.22
asm.js (Firefox 27)	3.24	3.00	4.00	1.51
Flash/Crossbridge (*)	5.16	4.16	7.81	2.41
asm.js (Chrome 33)	5.43	4.00	6.00	2.54
Java (1.8)	5.71	5.00	6.00	2.67
AS3	8.15	7.00	9.00	3.81
asm.js (IE11)	9.54	7.00	12.0	4.46
Dart (Dartium)	10.8	9.00	14.0	5.05
Box2dWeb (Firefox 27)	10.9	10.0	11.0	5.10
Box2dWeb (Chrome 33)	14.5	12.0	18.0	6.78
Box2dWeb (Safari 7)	15.5	13.0	19.0	7.24
Box2dWeb (IE11)	15.6	13.0	21.0	7.29
Dart2js (Chrome 33)	30.6	26.0	35.0	14.3
asm.js (Safari 7) (**)	272.	240.	309.	127.