Fix the podspec to work with current Cocoapods

In the current version of CocoaPods, clean_paths has been deprecated and now CocoaPods will clean any file not included in the sources, resources, etc properties. So, I removed the clean_paths option from the spec and reworked the source_files to make sure Support/ARCHelper.h was included.

Also, I'm not sure if I misunderstood, but as far as I can tell MOOPullGesture requires ARC, but the podspec specified that it does not. I reversed this.