Turn on edge anti-aliasing in iOS 7.0 and later

The edges of rotated views will now be smoother when rotated off-axis.
See http://confusatory.org/post/78059850721/easy-antialiased-calayer-edges-on-ios-7-0-and-later for more info.

Examples:

Without edge anti-aliasing:

![not-1](https://cloud.githubusercontent.com/assets/474/2533263/c7ceaba8-b557-11e3-8ec1-aa6c799585c0.png)

![not-2](https://cloud.githubusercontent.com/assets/474/2533264/caad660c-b557-11e3-9701-05324656893b.png)

With anti-aliasing turned on:

![on-1](https://cloud.githubusercontent.com/assets/474/2533265/d20e3d68-b557-11e3-82fd-be25018e6892.png)
![on-2](https://cloud.githubusercontent.com/assets/474/2533266/d433c298-b557-11e3-9fe4-665356b9b5b4.png)