Adding /proc check to rc.d/smbd

[David Brownlee <abs%absd.org@localhost>]

After a particularly unenjoyable session trying to work out why samba4
was not working on a NetBSD box before finally realising that was all
due to /proc not being mounted, it occurs to me that adding a check
for /proc being mounted to rc.d/smbd could save others that particular
slice of unenjoyment - even a warning message could be a real
benefit...

David