Brisbane failure Inventory has no attribute 'filter'

[Ian Clatworthy]

John Arbash Meinel wrote:
> Since Ian landed his "get the partial tree" part from Inventory.filter()
> it is now causing test failures because CHKInventory doesn't support
> filter().

I'll take a look. filter() doesn't mutate anything so it ought to fit in OK
over a CHKInventory. But the real goal is to get a filtered TreeDelta
back quickly from Repository.get_revision_deltas() and the best way of
doing that will undoubtedly be different in CHKInventories.

> I don't have a good idea of what you were thinking to get those tests
> passing again, so I would appreciate your assistance.

Sure. I'm hoping to put my "log DIR" patch back up today so I'm not
far aware from this area anyway.

Ian C.