Make _calculate_price available via utils.py

[Martin Fitzpatrick]

It would be helpful to have access to the _calculate_price function in a more accessible location for use in other models (on the fly conversion etc.) Please move the _calculate_price function to utils.py or similar.

Not a big issue but prevents ugly referencing into a private function / wraparound functions. Thanks

[Panos Laganakos (panosl)]

It didn't seem at the time that it would be useful outside of the templatetags, but if it's helpful to you anyone who wishes to make use of it, I'll make it more accessible.

[Martin Fitzpatrick (mfitzp)]

Thanks Panos, much appreciated.

[Panos Laganakos (panosl)]

Martin, please check rev. 13, and see if this works for you.