It's under Server Settings ... Settings. I think it's been there for some time now. The settings do different things. Enabling HTTP status codes means that CF will actually return a 500 error if there's a CF error. Without that enabled, CF will display error information to the user, but will return that within a regular page response with a 200 status code. This means that automated clients won't realize they've received an error in most cases, and it's not really standard behavior for application servers for this reason.
Enabling robust exception information means that you'll see more detailed error information, regardless of whether you've chosen to enable HTTP status codes or not. But you might run into a problem here. If you have IIS as your web server, you might see that IIS chooses not to return your full set of error information to the user. There are IIS settings that control what error information, if any, is returned. For debugging purposes, you can disable this, but it's disabled in IIS, not in CF, if I recall correctly.