[MiNT] Hiding filesystems

["Julian Reschke" <reschke@muenster.de>]

Hi,

as another test, I have hardwired SPIN's root directory to have a "hidden"
flag -- and all the software I use does what I expect:

-- Gemini by default does not show the entry in U:\
-- Mupfel's "ls" does not display the entry unless given the -a flag
-- df -a displays the filesystem

Maybe we should then discuss how to set the flag -- if we don't want to
change MiNT's behaviour to refuse Fattrib() on directories, we still can
invent a Dcntl opcode to do that...