Merge pull request #808 from benhuson/issue_777_pricing

Improvements to product currency and quantity discounts layout.
Remove the logic that replaces product images with site header images. Could not find any case where this would be useful.
In any case, the logic was faulty and caused product images to be removed on single product pagews
when using a WP theme that did not support header images.
Give the option to the theme to change the packing slip that is displayed or printed
Added some whitespace, some brackets and a prefix for the theme folder.
Merge pull request #812 from JeffPyeBrook/theme-the-packing-slip

Give the option to the theme to change the packing slip
added wpsc_the_featured_image_fix with deprecated message
Merge pull request #810 from JeffPyeBrook/no-theme-header-image-replace

Remove the logic that replaces product images with site header images.
Add filter to _wpsc_is_bot_user()