zen_get_category_tree no longer including 'Top' category when needed

[lat9]

With the zc158 update to move the definition of TOPMOST_CATEGORY_PARENT_ID into the non-db settings initialization, that value was changed from'0' to 0, changing its defined type.

That, unfortunately, rippled down into the admin so that

1. The coupon-restrictions page no longer includes the 'Top' category in its dropdown.
2. The copy_product admin sidebox no longer includes the 'Top' category in its dropdown (which it shouldn't unless there are already products in the top-level category).
3. The move_product admin sidebox now operates in the same manner as the copy-product one.
4. The 'Move category' sidebox no longer includes the 'Top' category in its dropdown, so you can no longer move a category's sub-category to the top-level.

Each of the above list of elements where the 'Top' category was missing-in-action was based on a variable-less call, e.g. zen_get_category_tree() flavored invocation.

Items 1 and 4 are corrected by simply restoring the TOPMOST_CATEGORY_PARENT_ID definition to its string type. Items 2 and 3 need some additional 'assistance' so that they don't offer the "Top" category as the location if there are not already products in the top-most category.