increase system-wide filename limit to 255

. move mfs-specific struct, constants to mfs/, so
	  mfs-specific, on-disk format structs and consts are
	  fully isolated from generic structs and functions
	. removes de and readfs utils

commands/writeisofs/writeisofs.c

@@ -36,7 +36,7 @@ typedef unsigned long int u_int32_t;
 #include <sys/types.h>
 #include <sys/stat.h>
 
-#define NAMELEN		(DIRSIZ+5)
+#define NAMELEN		(NAME_MAX+5)
 #define ISONAMELEN	12
 #define PLATFORM_80X86	0