Recompressed ApplyDiff() input on Diff() output
Recompressed ApplyDiff() input on Diff() output

In Diff(), if we noted that ApplyDiff() was given compressed data,
attempt to return compressed data ourselves, so that our callers don't
have to remember this stuff.

Signed-off-by: Nalin Dahyabhai <f562fcb2a0b898bf0be1afc867ea92325d8f825f@redhat.com>

rhatdan/storage,containers/storage,containers/storage,rhatdan/storage,containers/storage,rhatdan/storage