decouple Jehanne from 9P2000 (as much as needed)

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.

sys/src/lib/stdio/tmpnam.c

@@ -20,7 +20,7 @@ char *tmpnam(char *s){
 		while(*p=='9') *p++='0';
 		if(*p=='\0') return NULL;
 		++*p;
-	}while(access(name, 0)==0);
+	}while(access(name, AEXIST)==0);
 	if(s){
 		strcpy(s, name);
 		return s;