fixing billing accounts to allow splitting payments

[Si Chen-2]

Hi everybody -

I know there's been a bit of discussion lately about billing  
accounts.  I researched the code today and came up with this way to  
allow a billing account plus another method of payment on an order.  
Please see my notes on:
http://issues.apache.org/jira/browse/OFBIZ-93

and give me your comments.

Thanks,

Si