storageutil: consistently raise LookupError (API) The interface docs say this is supposed to raise LookupError on failure. But for invalid revision number input, it could raise IndexError because ifileindex.node() is documented to raise IndexError. lookup() for files isn't used that much (pretty much just in basefilectx in core AFAICT). And callers should already be catching LookupError. So I don't anticipate that much fallout from this change. Differential Revision: https://phab.mercurial-scm.org/D4798