Account for different reach limit in Survival/Creative. Fixes BUKKIT-4257

When we first added the reach limiter in CraftBukkit there was no
difference between how far the client could reach in vanilla while in
Survival or Creative. At some point in Minecraft's cycle Creative was
given a block extra to work with and our protection was not updated to
account for this. We need to respect the possibility of different game
modes in Minecraft providing the client with varying reach distances.