AFNetworking 2.0 support

[bezigon]

Once I added AFURLConnectionByteSpeedMeasure in CocoaPods, some problems were revealed:

../Pods/AFNetworking/AFNetworking/AFURLConnectionOperation.h:186:1: Property with 'retain (or strong)' attribute must be of object type
../Pods/AFNetworking/AFNetworking/AFURLConnectionOperation.h:191:1: Property with 'retain (or strong)' attribute must be of object type

Need some improvements in my opinion.

[OliverLetterer]

Feel free to submit a pull request :)

[bezigon]

I have lacking experience with method swizzling, and I have no idea where to look for.
But I'll try to spend time on it.

[natanrolnik]

@bezigon @OliverLetterer Do you have any idea on how to fix this?