Add performance optimization when there is only a single identification attribute in use. Switch to `compare:` instead of `localizedCaseInsensitiveCompare:` to speed up generation of cache keys.
Eliminate use of `NSCache` within `RKPropertyInspector`. Profiling in instruments reveals that use of `NSCache` is significantly slower than `NSMutableDictionary` for this performance critical code. refs #1232
Add an autorelease pool around the hot mapping loop in `RKMapperOperation` as significant time was being spent in autorelease during mapping and it appears to have a beneficial effect on performance. refs #1232