Image capture crashes on iOS7

I'm still investigating this, but I'm seeing issues where image capture at the end of each of my tests was causing the app to crash.

Unsure if this is a problem isolated to my app or not and so far I've only seen this on our CI build slave. Here's a backtrace:

```
Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0   WebCore                             0x072671bc -[TileHostLayer renderInContext:] + 44
1   QuartzCore                          0x01a61646 -[CALayer _renderSublayersInContext:] + 413
2   QuartzCore                          0x01a5fb8c -[CALayer renderInContext:] + 1483
3   QuartzCore                          0x01a61646 -[CALayer _renderSublayersInContext:] + 413
4   QuartzCore                          0x01a5fb8c -[CALayer renderInContext:] + 1483
5   QuartzCore                          0x01a61646 -[CALayer _renderSublayersInContext:] + 413
6   QuartzCore                          0x01a5fb8c -[CALayer renderInContext:] + 1483
7   QuartzCore                          0x01a61646 -[CALayer _renderSublayersInContext:] + 413
8   QuartzCore                          0x01a5fb8c -[CALayer renderInContext:] + 1483
9   QuartzCore                          0x01a61646 -[CALayer _renderSublayersInContext:] + 413
10  QuartzCore                          0x01a5fb8c -[CALayer renderInContext:] + 1483
11  CAN                                 0x0016e12f +[UIImage(Frank) imageFromApplication:resultInPortrait:] + 1520 (UIImage+Frank.m:61)
12  CAN                                 0x0016eaf0 -[ImageCaptureRoute handleRequestForPath:withConnection:] + 445 (ImageCaptureRoute.m:150)
13  CAN                                 0x0016a536 __53-[RequestRouter handleRequestForPath:withConnection:]_block_invoke + 53 (RequestRouter.m:68)
14  libdispatch.dylib                   0x03382444 _dispatch_barrier_sync_f_slow_invoke + 71
15  libdispatch.dylib                   0x033934b0 _dispatch_client_callout + 14
16  libdispatch.dylib                   0x03381766 _dispatch_main_queue_callback_4CF + 340
17  CoreFoundation                      0x039afa5e __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 14
18  CoreFoundation                      0x038f072b __CFRunLoopRun + 1963
19  CoreFoundation                      0x038efb33 CFRunLoopRunSpecific + 467
20  CoreFoundation                      0x038ef94b CFRunLoopRunInMode + 123
21  GraphicsServices                    0x03e9c9d7 GSEventRunModal + 192
22  GraphicsServices                    0x03e9c7fe GSEventRun + 104
23  UIKit                               0x01c9a94b UIApplicationMain + 1225
```

I'll update this issue as I get more information.