- Make use of the open intents to improve close-to-open
    cache consistency. Only force data cache revalidation when
    we're doing an open().

  - Add true exclusive create to NFSv3.

  - Optimize away the redundant ->lookup() to check for an
    existing file when we know that we're doing NFSv3 exclusive
    create.

  - Optimize away all ->permission() checks other than those for
    path traversal, open(), and sys_access().