Improve interoperability between CKRefreshControl and UIRefreshControl classes

[johnhaitas]

CKRefreshControl and UIRefreshControl can now be used interchangeably throughout the app.

Adds support for UIRefreshControl *refreshControl = [[UIRefreshControl alloc] init]; in iOS5.

[johnhaitas]

Thanks to @0xced's method here: https://github.com/0xced/NSUUID/blob/1.0.1/NSUUID.m#L167-L221

[bjhomer]

This looks awesome. I really wish I understood better what the inline asm is doing, but if @0xced says it works I'm inclined to believe him.

Does this provide complete support for using UIRefreshControl everywhere instead of CKRefreshControl? If there's no reason to use CKRefreshControl anymore, then maybe we should just recommend using UIRefreshControl always, and say "This is magic; just link against this library and UIRefreshControl will work on iOS 5!". We wouldn't even need to export any headers, if this is the case.

[johnhaitas]

I think we should recommend people use UIRefreshControl rather than CKRefreshControl - I am going to be doing that myself. That way no refresh control code needs to be changed when iOS 5 support is dropped from an app.

[0xced]

For full compatibility, I think you should use objc_duplicateClass(self, "UIRefreshControl", 0); instead of objc_allocateClassPair + objc_registerClassPair since this will add an intermediate CKRefreshControl class in the hierarchy.

[johnhaitas]

I deliberately took this approach rather than objc_duplicateClass so we can later test if UIRefreshControl is a subclass of CKRefreshControl. This was particularly useful with the +appearance proxy.

I used objc_duplicateClass for CKParagraphStyle.

[johnhaitas]

I borrowed the subclassing idea from @steipete's PSTCollectionView

@bjhomer would it be ok to acknowledge @0xced and @steipete in the README.md file?

[bjhomer]

I have no problem with that