Change AFNetworking import to allow framework build

[sammcewan]

Changing import to allow AFDownloadRequestOperation to be built as a framework.

[karolus]

Would help a lot

[steipete]

Is this really still being used? Why not go with NSURLSession?

[karolus]

I've found your solutions some time ago, worked well for me, until I wanted to switch do cocoa pods frameworks. But if you suggest that NSURLSessions it's better I'm going to look into it.