Ticket #33 (task)

Rewrite the TnyGtkHeaderListModel to use a GPtrArray in stead of a GList internally. This will greatly improve the sorting speed, and might reduce prepending speed. Try to keep the prepend fast and the append slow (if it has to be slow) (you might have sort or shift items after appending, you shouldn't have to sort nor shift when prepending).

Try to pre-allocate the size of the GPtrArray, as this will enhance prepending speed too.

Ticket #30 describes a race condition in the current GList-based code: try to solve this problem. A suggestion is to store the index of the GPtrArray in the iter->user_data in stead of a pointer to the TnyHeader instance (as how it's now). If the problem remains, this will make it much more easy to know about the instance's state.