MB-8020 Add advice call to OS layer

Will be ignored outside of linux for now, and only supports EVICT
(DONTNEED).

This adds a function to and bumps the version number of the file_ops
interface.

Change-Id: I6646d76c6bf72c2a3740df98e26c80902c7db3fc
Reviewed-on: http://review.couchbase.org/25605
Reviewed-by: Filipe David Borba Manana <fdmanana@gmail.com>
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: Aaron Miller <apage43@ninjawhale.com>