Process block cleanup first. Fixes BUKKIT-4103

When setting a block the server sets the new block ID, calls the cleanup
on the old block, then calls the placement logic for the new block. This
would normally work correctly but we have logic to prevent errors that is
causing one here. When trying to clean up the old block we notice the block
ID has changed and try to fix things, this causes the cleanup logic to
fail. To ensure cleanup happens correctly we now do all the cleanup before
changing the block which avoids triggering the fixup code.
Only delay removing containers. Fixes BUKKIT-5238

In commit f94b7af8 I delay removing the block until after running the
block's cleanup code to avoid errors. However, this causes problems of
its own due to blocks not being written with this in mind. To avoid blocks
getting recursively removed we now only delay removing containers since
they are the only ones we had problems with to begin with.
Merge pull request #2 from Bukkit/master

Merge changes from CraftBukkit:master