Auto Fill Seller Commission when Auto calculate is turned on.

I think it's important for the Seller to know how much he/she will be paid from selling his item, so I've gone ahead and enabled Auto-Fill when Auto-Calculate are both turned on in the Seller Settings.

Here's the code. The patch is created against my own custom Market Place, so I'm not sure if you're going to be able to apply it, but the code should still be relavent. Based of -beta4.