Smooth Boat pkt: overflow/invis objects

[turleypol]

Rewrite smooth boat pkt so it does not leak info of invisible objects. Send the correct objcount when truncating.
Testclient is now version 7
New tests:

• move a boat with a client on it while more items exists then the boat pkt can handle
• move a boat and check if the client gets the correct pos of boat and containing item

[coveralls]

Coverage increased (+0.5%) to 40.465% when pulling 2cb3b23 on boat_item_overflow into 2cb05d8 on master.

[KevinEady]

👍 LGTM