Merge branch 'v2.0-release' into v2.1-release

remove __orientationChanged listener on editbox destroyed (cocos#3464)

fix bmFontOriginalSize unable to display in prefab (cocos#3453)

* fix bmFontOriginalSize unable to display in prefab

* refine code

* refine code

should raise an exception if failed to initialize shaders (cocos#3329)

fix paveViewIndicator, blockInputEvent helpURL in engine (cocos#3285)

fix paveViewIndicator, blockInputEvent helpURL in engine (cocos#3285)

Fix cc.view._resizeWithBrowserSize typo (cocos#3130)

Fix return type should be vec2 instead of simple object for fireball/…

…issues/7898 (cocos#3046)

Improve doc for Node zIndex

fix the loadResDir function param transfer problem (cocos#2992)

fix loadResDir completeCallback absent issue