Change PLayerCollectionList to use a CopyOnWriteArrayList.
Revert "Change PLayerCollectionList to use a CopyOnWriteArrayList."

This reverts commit 8558b6a1c3dba845182391f29dfadb89015d4760.
Better pipe exiting
let injectItem add items with output unknown to the item list, moveSolids will drop them at the appropriate time.
Fix render derp on corners
Keep processing other items if we encounter a to-drop item
Drop to-drop items when they hit 0.75 progress