Add ability to plop on top of pins and abut fallthroughs

1. A dollop can not plop itself atop its own pin
2. Dollops that fallthrough to one another will now
   be properly aligned adjacent to one another even
	 if they are not coalesced by zipr-proper. This
	 basically gives the plugin the ability to preplace
	 fallthrough dollops consecutively without having
	 to trick zipr into doing it for them.