Clear out empty extended block ID array. Fixes BUKKIT-2923

If a chunk gets a block added to it that requires the extended block id
nibble array (block id greater than 255) the array is created and saved
with the chunk. When the blocks are verified to make sure they exist these
entries are erased but the extended block id array is not. This causes the
server and client to disagree about how much data a chunk has which makes
the client crash while trying to load the chunk for rendering.

To resolve these issues we now clear the extended block id array on chunk
load if there is no valid data in it.
Add crafting result slot for sheep breeding. Fixes BUKKIT-2926

Sheep now use the crafting system when breeding to determine what color
their baby should be. This triggers an event but the event wants the
crafting inventory to have a result slot which sheep do not have. This
event could be useful for plugins to control the output of sheep breeding
so instead of disabling it we add a result slot so the event fires without
issue.
Fixed some async tasks running synchronously. Fixes BUKKIT-2934

Additionally refactored cancel method to be more object-oriented.
Rework skull dropping. Fixes BUKKIT-2930 and BUKKIT-2820

Skulls need their tile entity in order to create an item correctly when
broken unlike every other block. Instead of sprinkling special cases all
over the code just override dropNaturally for skulls to read from their
tile entity and make sure everything that wants to drop them calls this
method before removing the block. There is only one case where this wasn't
already true so we end up with much less special casing.
Update tile entity on client on cancelled block break. Fixes BUKKIT-2935

When a client tries to break a block it assumes it has done so unless told
otherwise by the server. This means the client also wipes out any tile
entity data it has for the block as well. We do not send this data when
updating the client so clients lose things like text on signs, skull type,
etc when they aren't allowed to break the block.
Don't thread single chunk compression. Fixes BUKKIT-2927

Packet 51 is used to send updates about large changes to single chunks
and to remove chunks from the client when they get out of range. In the
first case a single packet object is created and queued for all relevant
players. With our current chunk compression scheme this means the first
player to have the packet processed will start the compression and get the
packet correctly but the rest will get garbage.

Since this packet never contains much data it is better to simply handle
compression of it on the main thread like vanilla does instead of putting in
locks and dealing with their overhead and complexity.
Remove fire ticks if damage has been canceled. Fixes BUKKIT-2933
Merge branch 'master' of git://github.com/Bukkit/CraftBukkit

# By Travis Watkins (5) and others
# Via feildmaster
* 'master' of git://github.com/Bukkit/CraftBukkit:
  Remove fire ticks if damage has been canceled. Fixes BUKKIT-2933
  Don't thread single chunk compression. Fixes BUKKIT-2927
  Update tile entity on client on cancelled block break. Fixes BUKKIT-2935
  Rework skull dropping. Fixes BUKKIT-2930 and BUKKIT-2820
  Fixed some async tasks running synchronously. Fixes BUKKIT-2934
  Add crafting result slot for sheep breeding. Fixes BUKKIT-2926
  Clear out empty extended block ID array. Fixes BUKKIT-2923