Jehanne is going to use a new file protocol, but Plan 9 is really
coupled with 9P2000.
Renamed fcall.h as 9P2000.h and introduced specific constants such
as NP_OREAD, NP_OWRITE and so on, so that we can use different values
in the kernel and new protocol.
Renamed devmnt to devninep, since it's actually a device serving 9P2000
file systems.
Also, fixed 9P2000 support in Jehanne, that was broken with the introduction
of OSTAT.
Giacomo Tesio