macos fsevents hinting

macos fsevents hinting

add support for faking it. no exported interface exists, sadly.
currently does only authentication events, and is best-effort only,
however for people who get tokens after viewing directories in finder,
this is a drastic improvement.

also adds needed setting to afssettings plist

FIXES 23781

Change-Id: I46d5a6cf103c30a2134decccc929e1ef85a26726
Reviewed-on: http://gerrit.openafs.org/451
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>