Fix calculation of base total in magento report with discount (#555)

* Fix calculation of base total in magento report with discount

Actually magento store discount with negative value :  - 10

If you have an order with subtotal = 90 and base_discount_invoiced = -10

When Magento do base_subtotal_invoiced  - base_discount_invoiced => 90 -- 10 => 90 +10 => 100

* Update fix

I think it's clearer with ABS value, like magento do for the other columns

Author: kpitn

app/code/core/Mage/SalesRule/Model/Resource/Report/Rule/Createdat.php

@@ -125,7 +125,7 @@ protected function _aggregateByOrder($aggregationField, $from, $to)
                 'total_amount_actual'     =>
                     $adapter->getIfNullSql('SUM((base_subtotal_invoiced - ' .
                         $adapter->getIfNullSql('base_subtotal_refunded', 0) . ' - ' .
-                        $adapter->getIfNullSql('base_discount_invoiced - ' .
+                        $adapter->getIfNullSql('ABS(base_discount_invoiced) - ' .
                         $adapter->getIfNullSql('base_discount_refunded', 0), 0) .
                         ') * base_to_global_rate)', 0),
             );