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

Mostly bug fixes and code sanitization motivated by the upcoming
support for Darwin hosts. Thanks to Keno Fischer.

# gpg: Signature made Thu 07 Jun 2018 11:30:56 BST
# gpg:                using RSA key 71D4D5E5822F73D6
# gpg: Good signature from "Greg Kurz <groug@kaod.org>"
# gpg:                 aka "Gregory Kurz <gregory.kurz@free.fr>"
# gpg:                 aka "[jpeg image of size 3330]"
# Primary key fingerprint: B482 8BAF 9431 40CE F2A3  4910 71D4 D5E5 822F 73D6

* remotes/gkurz/tags/for-upstream:
  9p: xattr: Properly translate xattrcreate flags
  9p: Properly check/translate flags in unlinkat
  9p: local: Avoid warning if FS_IOC_GETVERSION is not defined
  9p: xattr: Fix crashes due to free of uninitialized value
  9p: Move a couple xattr functions to 9p-util
  9p: local: Properly set errp in fstatfs error path
  9p: proxy: Fix size passed to `connect`

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