Error message returns "object Object" to user in alert

[alexdryden]

Summary: While testing a feature we are working on, we found a few places where alert messages sent to the user don't contain the custom error message.

Steps to reproduce:

• As a super user, open a book where you are not a book user
• Go to Content tab and select Add new page
• Add title and body and click "Save"

Behavior expected: Error message alert with text: "Something went wrong while attempting to save: You do not have permission to modify this book".
Behavior observed: Error message alert with text : "Something went wrong while attempting to save: object Object"

Message contents are here:

scalar/system/application/views/arbors/html5_RDFa/js/form-validation.js

Line 301 in a9165f1

alert('Something went wrong while attempting to save: '+message);

and here:

scalar/system/application/controllers/api.php

Line 111 in a9165f1

if (!$this->user && $this->api_users->is_super()) $this->_output_error(StatusCodes::HTTP_UNAUTHORIZED, 'You do not have permission to modify this book');

The pattern that I see elsewhere for this kind of message reporting is message.responseJSON.error.message[0].value; which gets the message contents from the jqXHR response object, and I can submit that as a pr with the fixes for the other error message reporting bug if that looks good to you.

[craigdietrich]

A pull request would be excellent, thanks @alexdryden !