Disable portal support for entities for now. Restore allowNether check.

Relates to:
BUKKIT-2695 BUKKIT-2675
[Bleeding] Prevent players from appearing to be sneaking after they change dimensions whilst doing so.
Remove Anvil debug. Fixes BUKKIT-2732
[Bleeding] Implement new Hanging events. Adds BUKKIT-2754
[Bleeding] Fire damage is no longer a valid reason for hanging entity removal
Implement the API for ItemFrames. Adds BUKKIT-2668
Hook command block up to ConsoleCommandSender. Fixes BUKKIT-2684

This will need to have its own CommandSender but this makes command blocks
work for now with any command console can run.
Expose API for managing and using GameRules. Adds BUKKIT-2757
Use BlockCommandSender for dispatching Command block commands

Also allow commands that don't start with a / to match vanilla behavior
Implement API for ambient mob spawn limit. Add spawn-limit.ambient to
bukkit.yml. Adds BUKKIT-2765
Fix NPE when blowing up an item frame. Fixes BUKKIT-2763
Add inventory and slot types for new containers. Fixes BUKKIT-2741
Fire HangingBreakEvent when explosions remove hanging entities. Fixes BUKKIT-2764
Updated version to 1.4.2-R0.1 in pom.xml for Beta.
Updated version to 1.4.2-R0.2-SNAPSHOT for development towards next release.
Change ItemFrame to actually provide a defensive copy. Fixes BUKKIT-2784

If a defensive copy is not used in the API, changes to the item are
reflected in memory, but never updated to the client. It also goes
against the general contract provided in Bukkit, where setItem should be
the only way to change the underlying item frame.
Add CraftArt mappings for Wither. Fixes BUKKIT-2667.

The static assertions are not normally evaluated in the JVM, and failed
to fail when the enums went from size 25 to size 26. This meant missing
values would not be detected at runtime and instead return null,
compounding problems later. The switches should never evaluate to null
so will instead throw runtime assertion errors.

Additional unit tests were added to detect new paintings and assure they
have proper, unique mappings. The test checks both that a mapping
exists, is not null, and does not duplicate another mapping.
Delegate recreateStructures to nms provider. Fixes BUKKIT-2760

This was a miss when updating to 1.4.2
Fix compile issue with chunk generation.
Improved the potion test to detect missing PotionType values.