Adding two request descriptors for a given class in Restkit 0.2

You can use a dynamic mapping to switch the serialization behaviors. If this is a common enough issue, we could conceivably add path matching to the request descriptor. I just have not had a ton of requests for such a feature.

There is an example of how to use the dynamic mapping with a request in the unit tests: https://github.com/RestKit/RestKit/blob/master/Tests/Logic/ObjectMapping/RKObjectParameterizationTest.m#L495-L534