Fix bug 826444: Disable "fullscreen" section editing.

Since we've decided the only way we want to support section editing is
through the inline AJAX-y edit, this disables the ability to do it
through any other kind of request, and updates the section-editing
unit tests to match that.
Merge branch 'master' into section-edit-inline-only
Wrap error message in gettext.
Merge pull request #814 from ubernostrum/section-edit-inline-only

Fix bug 826444: Disable "fullscreen" section editing.