Attempting to edit untranslated page fails without notice

Problem/Motivation

If I am viewing a page in the website's original language (English in this case) on a website which has a paid GTranslate account, and attempt to edit the page, the page reloads without any notice that I am viewing untranslated page. This makes it seem like GTranslate is failing to connect, when it's actually just user error.

It would be better if GTranslate module displayed a message reminding me that I am viewing an untranslated page and that there is nothing to edit.

Steps to reproduce

1. Go to an English-language page on my English-language website.
2. Add ?language_edit=1 to the URL in the location bar
3. Press Enter

Desired result: I get a message that the page is not machine translated and that there is nothing to edit.

Actual result: The page reloads with no feedback about why GTranslate didn't do anything.

Proposed resolution

Display an error message "This page view is not machine translated. There is nothing to edit."

Remaining tasks

User interface changes

API changes

Data model changes