7.0 update price

Hi Giovanni,

thought I'd go this through one last time. I hope you don't mind having a go at your code but I wanted to clean up this particular method a little bit with its many indents and a bit of code duplication. I got the method down from 102 lines to 65 lines. I also made the user visible help text a bit easier to digest, and caught one more supplierinfo.product_id reference taken to be a product.product, not template.