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
Update CraftBukkit to Minecraft 1.4.5.
Update tile entity when interact event is cancelled.

If a plugin cancels a PlayerInteractEvent when left clicking a block the
client may have removed this block if they are in creative mode or if the
block breaks in a single hit. In this case, we need to update the client's
tile entity as well as telling it the block still exists.
Use synchronous calls and wait for chat disconnect. Fixes BUKKIT-2946

When invalid chat is detected we currently drop the connection with no
hint as to why as anything else is not allowed while we're off the main
thread. To give valid disconnect reasons and fire proper events instead
pass these off to the main thread and wait for it to process them.
Ignore empty custom payload packets. Fixes BUKKIT-2957
Don't create tile entity when block placement fails. Fixes BUKKIT-2924

End portals can only be placed in the end during the dragon's death.
Attempts to place them outside of this window causes the block to remove
itself. However, we still create the tile entity for the portal which
leads to exceptions spamming the console about a tile entity existing
without the appropriate block. In these cases we should not place the tile
entity at all.
Don't wait for main thread when processing commands.

In order to correctly handle disconnects for invalid chat we setup a
Waitable and pass it to the main thread then wait for it to be processed.
However, commands are also chat packets and they are already on the main
thread. In this case, waiting will deadlock the server so we should just
do a normal disconnect.
Spigot changes for 1.4.4
Merge commit '63acbb4382c94ce739aec757f3659dbc086eec7e'