Bug 9797 - Untranslatable strings have returned to ajax.js

Bug 9797 - Untranslatable strings have returned to ajax.js

The patch for Bug 8942 undid the changes to ajax.js made by Bug 9331.
This patch puts those changes back.

To test that preference-related error messages continue to work,
open the system preferences editor in two tabs. Log out in one tab and
try to save a system preference in the other. You should see correct
error messages.

Signed-off-by: Pierre Angot <tredok.pierre@gmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>