Don't skip ticks of entities at edge of chunks.

This adds a lost patch which was added back during 1.5.2
More info can be found from original commit
MinecraftPortCentral/MCPC-Plus-Legacy@b967858555b90ba93a47694d384a82afb8f966c2
Merge branch 'master' of https://github.com/MinecraftPortCentral/MCPC-Plus
Removing broken chunk caching from World. Fixes BUKKIT-5425

Chunk caching in the World class does not know about outdated cache
values. This caused various problems when accessing previously unloaded chunks.
The caching also did not improve the performance so it is removed.
Synchronization is also not necessary, because all accesses to getChunkAt
may only come from the main thread.