[C] Call EntityChangeBlockEvent for boats destroying blocks

The Issue:
If a boat collides with a lily pad or a snow layer, it simply removes them. No event is thrown at the moment.

Justification for this PR:
We have the EntityChangeBlockEvent, which fits for this case. So plugins can listen for this event and maybe cancel it.
A plugin could do whatever it's wants to do, like simply pass the boat throw the lily pads, destroy the boat or drop snow balls for snow layers.

PR Breakdown:
This PR is calling EntityChangeBlockEvent. If a plugin cancels the event, the block isn't set to air.

Testing Results and Materials:
This code is running fine on our server and is just updated for the 1.5.1 changes in EntityBoat.

Relevant PR(s):
-

JIRA Ticket:
BUKKIT-3871 - https://bukkit.atlassian.net/browse/BUKKIT-3871