Update API for Acacia & Dark Oak. Fixes BUKKIT-4988

When Minecraft 1.7 was released, Acacia and Dark Oak TreeSpecies were
added. While Bukkit added them to TreeSpecies it did not add support in
getSpecies() and setSpecies().

Currently Acacia (0x4) is reported as Oak (0x0) and Dark Oak (0x5) is
reported as Spruce (0x1). This commit fixes that by updating the
respective functions with new bit checks.