Reorder combining-class to better suit Arabic shadda mark-mark positioning

Reorder combining-class to better suit Arabic shadda mark-mark positioning

As reported by Khaled on the list:

"After the introduction of canonical reordering of combining marks
(commit 34c22f8), I'm no longer able to do mark/mark substitution or
positioning for mark sequences that involve shadda as a first mark (or
most interesting sequences at least).

"After some digging, it turned out that shadda have a ccc=33 while most
Arabic marks that combine with it have a lower ccc value, which results
in the shadda being reordered after the other mark which,
unsurprisingly, breaks my contextual substitution and mkmk anchors."

See:

http://unicode.org/faq/normalization.html#8
http://unicode.org/faq/normalization.html#9