make  an empty array so implode doesn't fail
add wpsc_purchase_log_csv hook so we can do fun stuff before a CSV download
Use methods instead of accessing properties directly
Don't use wp_convert_bytes_to_hr() deprecated function. Fixes #508.

As per http://core.trac.wordpress.org/ticket/19067, WordPress 3.6 deprecates the wp_convert_bytes_to_hr() function in favour of the size_format() (which was was added in WordPress 2.3).
Fix warning in coupons admin if no order query in URL.
Fix typo in variable function, also, totally fix disabled/readonly issue.

Missed a spot.
Turns out disabling mandatory boxes, while checked, causes them to not be submitted.  This is a problem.

Readonly gives the same effect, but POSTs them properly.