Fix some issues introduced in v1.2

[pandamicro]

Changes proposed in this pull request:

• https://github.com/cocos-creator/fireball/issues/3919: Fix mouse hovered node access issue during scene switch
• Fix event.target not set in emit
• https://github.com/cocos-creator/fireball/issues/3927: break batch for scale9sprite with distortion
• https://github.com/cocos-creator/fireball/issues/3953: Only send one touch cancel event when ScrollView scrolled
• Fix small API issues

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@cocos-creator/engine-admins

[jareguo]

LGTM

[nantas]

lgtm