Fixed lighting burn calculation in MC 1.5.x

The old one didn't work with 1.5.x as under certain circumstances block.getLightFromBlocks() would return 14 even though the player was completely undercover. Particularly well lit ladders, trapdoors, sugar cane farms and a few other scenarios caused problems.

Modified it to use a combination of block.getLightLevel() and block.getLightFromSky() and everything seems to be working fine. We've been running it for nearly a week now with no further complaints!