GET/HEAD object with an explicit versionId that does not exist returned
NoSuchKey. AWS S3 returns NoSuchVersion (404) for this case; tools that
distinguish "key gone" from "this version gone" rely on that code.
Add the ErrNoSuchVersion error code and use it on the GET and HEAD
specific-version lookups. Only a genuine not-found maps to NoSuchVersion;
a transient or internal filer error now maps to InternalError (500)
instead of a misleading 404. getSpecificObjectVersion wraps its lookup
error with %w so callers can detect filer_pb.ErrNotFound.
Chris LuandGitHub
0e35235908