[Bleeding] Ensure skeletons spawn with equipment. Fixes BUKKIT-2836

Previously, when a skeleton was spawned via the spawn(...) function, the
resulting skeleton had no equipped bow and therefore could not properly
attack. This fix gives all skeletons the proper equipment and ensures that
they are able to attack.

(cherry picked from commit a2d90d3e30db2bf2897f19ff0b93461dfc8a487f)