Add onCall(n) and friends to SinonStub definition

These were added in Sinon 1.8, and the definition claims to be Sinon
1.8.1

From documentation:
"As of Sinon version 1.8, you can use the onCall method to make a stub
respond differently on consecutive calls."

http://sinonjs.org/docs/
verified + found a missing signature (for a seperate PR)

![image](https://cloud.githubusercontent.com/assets/874898/3347737/70edac84-f8f6-11e3-849e-fe524bb2f21d.png)