[RFC] deprecate InventoryEntry put_on_disk and get_tar_item

[Ian Clatworthy]

I need to refactor the export code as part of the next
round of content filtering enhancements. Right now, the
various exporters (except the zip one) delegate to the
InventoryEntry subclasses to do some of the work.
IIRC, there was a 'reduce the complexity of InventoryEntry'
drive some time back with a goal of one day eliminating it.

Any objections if I move the interesting code into the exporters
and deprecate the matching methods in InventryEntry? I want
to at least move the code, so the question is more one of
"Should I deprecate while I'm at it?".

Ian C.