Bug 9141 - Untranslatable strings on "pay an amount..." page

Bug 9141 - Untranslatable strings on "pay an amount..." page

Moving text of an error message from the script into the
template. To test, submit an amount which is greater
than the amount due. You should see an error message
displayed correctly with a properly-formatted currency
amount.

Signed-off-by: Marc Veron <veron@veron.ch>
Patch behaves as expected.

Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>
Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>