Merge pull request #404 from khawkins/unstable

Mobile SDK: master to unstable merge
added possibility to cancel SFRestRequests be forwarding cancel message to associated RKRequest object
Merge pull request #405 from bytefreak/unstable

added possibility to cancel SFRestRequests
Miscellaneous updates

- Some changes to OAuth to allow for better future ease of unit testing.
- Picked off a number of low hanging fruit warning updates, to clean up the project(s).