Showing error detail

Normally when a request fails the app shows a short, generic message and the real detail goes to the activity log. With this on, that real message and where it happened come back in the app too. It is meant for diagnosing a problem that only shows up against your live WHMCS, where the log may be awkward to reach. Turn it on, reproduce the problem once, read the message, then turn it back off so customers never see internal detail.