fixed prices for different currencies

[michael_s]

Fixes for small problems in the fixed_prices contribution.

Fixes:
1. When copying a product the fixed prices are copied incorrectly.
2. The variable $ajout_prix is built twice. The second time is done incorrectly. It is also redundant. Remove it.
3. The variable $product_prices_array is left undefined when the fixed_prices table is empty, resulting in error on OSCommerce pages. Fix by initializing the variable at all times.
4. Include example of how to import the prices for the default currency.

Problems left unfixed:
A. When editing a product the preview will not show the price. This could be fixed by previewing the price in the store's default currency.
B. The install instructions contain a few replacements where the only change is to add code that is commented out. These changes could be removed.
C. This contribution breaks specials. This could be fixed by adding a per-currency specials table.
D. This contribution breaks the JavaScript on the product edit page that updates the Products Price (Gross) field. This could be fixed by updating the Gross field based on the store's default

More...