fsck: actually detect bad file modes in trees

We use the normal tree_desc code to iterate over trees in fsck, meaning we only see the canonicalized modes it returns. And hence we'd never see anything unexpected, since it will coerce literally any garbage into one of our normal and accepted modes. We can use the new RAW_MODES flag to see the real modes, and then use the existing code to actually analyze them. The existing code is written as allow-known-good, so there's not much point in testing a variety of breakages. The one tested here should be S_IFREG but with nonsense permissions. Do note that the error-reporting here isn't great. We don't mention the specific bad mode, but just that the tree has one or more broken modes. But when you go to look at it with "git ls-tree", we'll report the canonicalized mode! This isn't ideal, but given that this should come up rarely, and that any number of other tree corruptions might force you into looking at the binary bytes via "cat-file", it's not the end of the world. And it's something we can improve on top later if we choose. Reported-by: Xavier Morel <xavier.morel@masklinn.net> Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>