[Bleeding] Add experimental support for entity portal traveling

EntityPortalEvent is called when an entity is about to portal to a
new location. This event is cancellable on top of being able to
change the exit location.

EntityPortalExitEvent is called when exiting the portal, allowing
for adjustment of the exit velocity.
Improve javadoc in 26 files.

Addresses:
BUKKIT-1643, BUKKIT-1868, BUKKIT-1846, BUKKIT-2632, BUKKIT-3196,
BUKKIT-3187, BUKKIT-3198, BUKKIT-3200, BUKKIT-3201 and BUKKIT-3417.
Don't try listing something that may not exist. Fixes BUKKIT-3471

The player name may not be provided, in which case the command will
fail hard.
Only use TravelAgent if supplied; Addresses BUKKIT-3466

If there is no TravelAgent assigned, it can not be used.
Fix invalid integers in spawnpoint command. Fixes BUKKIT-3509

getInteger returns min value on illegal number formats, so we change
behavior to throw an exception when requested.
Merge branch 'master' of git://github.com/Bukkit/Bukkit.git