Fix error message for readFile's open and return for execution context. Let exceptions be thrown from callbacks.
Fix error message for readFile's open and return for execution context. Let exceptions be thrown from callbacks.

huang-x-h/backbone.layoutmanager,tbranyen/backbone.layoutmanager,huang-x-h/backbone.layoutmanager,tbranyen/backbone.layoutmanager,SimenB/backbone.layoutmanager,GerHobbelt/backbone.layoutmanager,SimenB/backbone.layoutmanager