Remove Util.pcequiv() and stop pretending Java colls are equiv to Clojure colls

The Util.pcequiv() method

static public boolean pcequiv(Object k1, Object k2){
	if(k1 instanceof IPersistentCollection)
		return ((IPersistentCollection)k1).equiv(k2);
	return ((IPersistentCollection)k2).equiv(k1);
}

tries to get equiv semantics (cross-class number equality) for cases of mixed Clojure/Java collection comparison. However, this is not a sustainable direction and we would like to stop doing this.

Attached patch removes this and changes calling code to only call equiv when both collections are IPersistentCollection.