Owl: Add an offset to the "is_above_player()" method.

Owl: Add an offset to the "is_above_player()" method.

This way it is more likely that the thrown object will hit Tux. Also, the
standard "collision_player()" method from BadGuy will be used. There's no need
for the hack copied from the "Kamikaze Snowball".

git-svn-id: http://supertux.lethargik.org/svn/supertux/trunk/supertux@6563 837edb03-e0f3-0310-88ca-d4d4e8b29345