Need to be able to replace nonexistant files in order to do proper backup/restore or import/export

[jpmccu]

If a depot is being stored locally, obviously the backup and restore can just use local archiving tool. But if they're remote and someone wants to either export the depot to another installation or do some other sort of extraction, we need to be able to replicate depots exactly, including ID. One easy way to do this is to allow fileids to optionally be set on create.

This is needed because if the database is storing file ids, then it would break everything to have the new store use a new ID.