Add a cache in RKCompoundValueTransformer for source/destination class pairs, so that the subset of matching transformers does not have to be calculated every time.  This is a significant time savings while mapping.
Add a cache in RKCompoundValueTransformer for source/destination class pairs, so that the subset of matching transformers does not have to be calculated every time.  This is a significant time savings while mapping.

RestKit/RKValueTransformers,0xced/RKValueTransformers