* master: (118 commits)
  nodefs: split the dual function of OperationStubs
  nodefs: regularize method naming
  nodefs: test Mknod
  nodefs: by default return input offset for Lseek
  nodefs: rename DefaultOperations to OperationStubs
  nodefs: doc nits.
  nodefs: port utimens and allocate from fuse/nodefs
  fuse: add cancel channel to Release call
  nodefs: provide Inode.Root rather than Inode.IsRoot
  nodefs: drop InodeOf
  nodefs: embed Inode directly in DefaultOperations
  nodefs: fix outdated comment
  nodefs: fix double syscall.Close
  splice: more verbose panic if discarding pipe pair fails
  nodefs: document ToErrno, NewListDirStream
  nodefs: only set default timeout if Entry/Attr does not specify a timeout
  fuse: add Timeout methods to EntryOut and AttrOut
  nodefs: return ENOTSUP rather than ENOSYS
  nodefs: make everything compile on darwin
  nodefs: use syscall.Errno instead of fuse.Status
  ...

Provide InodeLink/InodeEmbed which implements linking machinery.

This is unlikely to be useful, but makes the API more uniform.

Use this to simplify loopbackNode.

This is an implementation detail, but it saves an indirection

syscall.Close is not safe to run twice. Reused fds cause random things
to break.

Test Lseek together with FOPEN_DIRECT_IO, and document this use-case
in directio_test.go