It now imports the whole file without user interaction, this
required adding a new concept of supplier availability to the
stock table. Other changes include: allowing existing users to be
selected from the sell page, their payment can also be delayed by
selecting the "account" option during the sale. Purchasing
variable priced items now calculates a base price depending on the
purchaser's buyer group. This is the amount the supplier is credited
for. The purchase page can now remain open for multiple purchasing
days by using a comma separated list for "co-op-day".