fixing error from bridge casting when compiling AFNetworking in an iOS Framework

For a reason I couldn't understand, when compiling the AFNetworking HTTPClient inside an iOS Framework, an error would come up in the initWithBaseURL method because of the lacking __bridge keywords.

I've added a screenshot showing the error message in the XCode logs

![screen shot 2013-05-14 at 11 39 30 am](https://f.cloud.github.com/assets/528492/500596/bc10b72e-bc7a-11e2-9986-dba3478dd4a0.png)