In 7639179cdf we swapped JSONKit for NSJSONSerialization.  I don't know why.
It used to be the case that JSONKit outperformed NSJSONSerialization, but
that gap is either much closer or reversed (depending on who's benchmarks
you believe) with iOS 7.

JSONKit also seems to be abandoned upstream.

http://stackoverflow.com/questions/16218583/jsonkit-benchmarks
https://github.com/johnezang/JSONKit/issues/133

This cset changes back to using NSJSONSerialization.  We'll see if anything
breaks.

Revert "Fix JSONKit serialization to accept subclasses of the basic types."
Revert "Swap in JSONKit"

This reverts commit 15ea71308e392dbe75694ce0d4338f02759049c7.
This reverts commit 7639179cdf2e8c2762957ca456e9a06438432836.

Conflicts:
	MKNetworkKit-iOS/MKNetworkKit-iOS.xcodeproj/project.pbxproj
	MKNetworkKit/MKNetworkOperation.m
Change setResponseJSON to return a BOOL.

This matches Apple coding conventions (having a non-void result
rather than relying on the NSError** parameter).