When program builds a large list and then sorts it's usually just as efficient to sort the list elements on insertion. This patch adds a function list_add_sorted and modifies db_loadpkgs to use it. It makes the function cleaner and removes the realloc/array kludge.

Timing tests of 'pacman -Q' showed no real change for 200 runs.

I can attach further patches to modify the other list_sort usages if this meets approval.