maximum ammount for coupon functionality added

I had a couple of clients request this feature so I rolled it into the core.  

Basically the clients wanted to cap the amount they were willing to discount.

If a customer had a coupon for 30% off.  They didn't want them to be able to use it if the total cart/item was over $200.   (thus caping the discount at $60 for a 30% off coupon of this setting).  etc.

I pretty much cloned the style/usage of the minimum spend functionality changing only the logic in class-wp-coupon.php to be LESS than the amount checked.  

I've seen a good number of folks requesting this on forums and my two clients currently.   Figured it'd be useful.

Any and all feedback welcome!