search: prevent SQL injection

Signed-off-by: Pierre-Alexandre Meyer <pierre@ning.com>
util: add system tag definition support to tag search

Signed-off-by: Pierre-Alexandre Meyer <pierre@ning.com>
refund: use correct payment method id to retrieve the plugin

Make sure to use the payment method id used by the original payment
when retrieving a refund info.

Signed-off-by: Pierre-Alexandre Meyer <pierre@ning.com>
NEWS: update for 0.8.11

Signed-off-by: Pierre-Alexandre Meyer <pierre@ning.com>