if first argument is string, second argument is 0/missing, searches for
a object that id(name) = 1 in this object inventory and this object's
environment's inventory. Returns the found object.
if first argument is string, second argument is object, only searches
for traget in that object's inventory.
"foo 1" means the first "foo" in the inventory. the first in the
inventory is the last object that moved in.
if first argument is object, second argument is 0/missing, check if
object is in this object's inventory, or as a sibling in this object's
evnironemnt's inventory, returns object's parent. // FIXME: this looks
like a mis-feature.
if first argument is object, second argument is object, check if
object1 is in object2 inventory, return object1 if true.
If object is hidden (via set_hide()), and current object is not hid‐
able. returns 0