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.