Closed #4453: cc.Sprite supports creating a sprite through URL
Fixed #4453: remove some invalid codes of cc.EditBox
Merge pull request #1706 from pandamicro/develop-3.0

Fixed #4456: Use undefined check in cc.loader and fix comment errors
Fixed #4453: add serverImg loader to support preloading image from other server.
Merge branch 'develop-3.0' of git://github.com/cocos2d/cocos2d-html5 into Iss4453_URLSprite

Conflicts:
	CCBoot.js
Merge pull request #1707 from dingpinglv/Iss4453_URLSprite

Closed #4453: cc.Sprite supports creating a sprite through URL
Warning about missing project.json

Warn the developer when project.json cannot be loaded or parsed.
Merge pull request #1709 from NatWeiss/patch-5

Warning about missing project.json
Fixed #4487: Add retina display support to CCDomNode
Merge branch 'develop-3.0' of git://github.com/cocos2d/cocos2d-html5 into develop-3.0