this is basically copy of what nfs_kq.c does - a thread periodically
polls server checking if any of the wateched files changed
eventually this should be changed to take advantage of SMB Directory
Change Notify
* g/c unused members 'mount_point', 'root_path', which only take space
* rename 'dev' to 'dev_fd' to more closely match what it is
* add 'export' member to avoid changing this again if ever smbfs would
be made exportable
bump SMBFS_VERMIN - ABI/API change; mount_smbfs needs to be recompiled
to work again