Fixed Orchid_CouponFix_Model_Observer for Magento 1.7+

Observer.php

<?php
class Orchid_CouponFix_Model_Observer
{
    public function cancel($observer)
    {
        $resource = Mage::getModel('core/resource');
        $db = $resource->getConnection('core_write');
        $event = $observer->getEvent();
      	$order = $event->getPayment()->getOrder();
        if ($order->canCancel()) {
            if ($code = $order->getCouponCode()) {
                try {
                    $coupon = Mage::getModel('salesrule/coupon')->load($code, 'code');
                    $coupon->setTimesUsed($coupon->getTimesUsed() - 1);
                    $coupon->save();
                } catch(Exception $e) {
                    Mage::log('Could not decrease usage by 1 for coupon ' .$code . '; ' . $e->getMessage());
                    return;
                }
                try {
                    $couponRule = Mage::getModel('salesrule/rule')->load($coupon->getRuleId(), 'rule_id');
                    $couponRule->setTimesUsed($couponRule->getTimesUsed() - 1);
                    $couponRule->save();
                } catch(Exception $e) {
                    Mage::log('Could not decrease usage by 1 for coupon rule ' .$coupon->getRuleId(). '; ' . $e->getMessage());
                }

                $customerId = $order->getCustomerId();
                if($customerId && $couponRule) {
                    try {
                        $customerCoupon = Mage::getModel('salesrule/rule_customer')->loadByCustomerRule($customerId, $couponRule->getId());
                        if ($customerCoupon) {
                            $customerCoupon->setTimesUsed($customerCoupon->getTimesUsed() - 1);
                            $customerCoupon->save();
                        }
                    } catch(Exception $e) {
                        Mage::log('Could not decrease usage by 1 for customer coupon ' . $code . ' / ' . $coupon->getId() . ' / ' . $customerId . '; ' . $e->getMessage());
                    }
                    try {
                        $couponUsage = $db->fetchOne($db->select()->from('salesrule_coupon_usage','times_used')->where('customer_id = ?', $customerId)->where('coupon_id = ?', $coupon->getId()));
                        $where = array(
                            $db->quoteInto('coupon_id = ?', $coupon->getId()),
                            $db->quoteInto('customer_id = ?', $customerId)
                        );
                        if($couponUsage <= 1) {
                            $db->delete('salesrule_coupon_usage', $where);
                        } else {
                            $db->update('salesrule_coupon_usage', array('times_used' => $couponUsage - 1), $where);
                        }
                    } catch(Exception $e) {
                        Mage::log('Could not decrease usage by 1 for customer coupon usage ' . $code . ' / ' . $coupon->getId() . ' / ' . $customerId . '; ' . $e->getMessage());
                    }
                }
            }
	    }
    }
}

Someone can use db table prefix and the queries used into example above will not work.
You have to change all the query syntax.
For example:
$db->delete('salesrule_coupon_usage', $where);
change to:
$db->delete($resource->getTableName('salesrule_coupon_usage'), $where);