[C] Call VehicleDestroyEvent when a boat is destroyed by fall damage. Fixes BUKKIT-5500

### The Issue:
When a boat is destroyed by fall damage, no event is fired, and the destruction can not be cancelled. 

### Justification for this PR:
Without this PR the VehicleDestroyEvent does not fire when a boat is destroyed by fall damage, although it obviously should fire.

### PR Breakdown:
This commit fixes the issue by firing the event and cancelling the destruction if the event is cancelled.

### Testing Results and Materials:
A testing plugin is provided, that will cancel all VehicleDestroyEvents. To reproduce the bug/fix build shomething like this: http://image.cubeside.de/uploads/2014/03/i1071b3pf30.png and drive down the waterfall with a boat onto the floor. Without this fix the boat will be destroyed and no event will be called. With this fix the event is called and it is possible to cancel the destruction of the boat.
Testing plugin: http://www34.zippyshare.com/v/30735483/file.html

### JIRA Ticket:
BUKKIT-5500 - https://bukkit.atlassian.net/browse/BUKKIT-5500