Add a private function to allow for BlockAssembler to properly
account for package information in CBlockTemplateEntry
Depends on D2863
CFeeRate uses division.
Yeah, it's not the number of dependencies unless it's a linear chain, but in some cases it won't be the number of dependencies even for that. I don't have a better definition of it.
The basic idea is that if sorted by Order the list would be ~ topologically valid. The idea is that transactions of lower order should go in before higher order ones.