Chicken should not block units

[elexis]

Since the new pathfinder, units make a big leap around obstructions instead of breaking the formation apart. This is very useful, since units now avoid the forest instead of getting entangled there. But being blocked by chicken near the CC is very hindering, especially in the beginning of the match.

Berries have become passable in r8899, see ​http://trac.wildfiregames.com/changeset/8899/ps/trunk/binaries/data/mods/public/simulation/templates/template_gaia_flora_bush.xml

So I propose to make chicken ghosts too, would help a lot and not really look bad.