leak fixed with GCG under iOS 6.0.

https://github.com/CocoaPods/Specs/issues/1730
https://github.com/BradLarson/GPUImage/issues/1748
It's not working like what I thought.
Leak fixed if worked with cocoapods.

https://github.com/BradLarson/GPUImage/issues/1748
https://github.com/CocoaPods/CocoaPods/issues/1001
Merge pull request #1751 from demon1105/master

leak fixed when worked with cocoapods.