Fix error reporting for API requests in the commits view and elsewhere.
The commits view wasn't showing any error responses when failing to

create a review request. It now displays an alert and clears the

spinner.
While working to fix this, I realized our error handling wasn't correct.

We weren't taking in the correct parameters in syncOptions.error that

RB.apiCall passes, and we weren't passing the arguments that Backbone's

wrapError expects. This now wires everything up so that errors coming

from the server will be properly represented in error handlers.

Triggered an error with a commit in the New Review Request page. Instead

of spinning forever, I saw an alert with the error message, and the spinner

stopped. I was then able to post a new commit.
Unit tests pass (except one failure unrelated to this change).