Merge remote-tracking branch 'remotes/gkurz/tags/for-upstream' into staging

Various bugfixes and code cleanups. Most notably, it fixes metadata handling in
mapped-file security mode (especially for the virtfs root).

# gpg: Signature made Tue 30 May 2017 14:36:22 BST
# gpg:                using DSA key 0x02FC3AEB0101DBC2
# gpg: Good signature from "Greg Kurz <groug@kaod.org>"
# gpg:                 aka "Greg Kurz <groug@free.fr>"
# gpg:                 aka "Greg Kurz <gkurz@linux.vnet.ibm.com>"
# gpg:                 aka "Gregory Kurz (Groug) <groug@free.fr>"
# gpg:                 aka "[jpeg image of size 3330]"
# gpg: WARNING: This key is not certified with a trusted signature!
# gpg:          There is no indication that the signature belongs to the owner.
# Primary key fingerprint: 2BD4 3B44 535E C0A7 9894  DBA2 02FC 3AEB 0101 DBC2

* remotes/gkurz/tags/for-upstream:
  9pfs: local: metadata file for the VirtFS root
  9pfs: local: simplify file opening
  9pfs: local: resolve special directories in paths
  9pfs: check return value of v9fs_co_name_to_path()
  util: drop old utimensat() compat code
  9pfs: assume utimensat() and futimens() are present
  fsdev: fix virtfs-proxy-helper cwd
  9pfs: local: fix unlink of alien files in mapped-file mode
  9pfs: drop pdu_push_and_notify()
  fsdev: don't allow unknown format in marshal/unmarshal
  virtio-9p/xen-9p: move 9p specific bits to core 9p code

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>