netbsd dirent.h, import sys/sys *.h, mfs cleanup

. add all sys/sys headers not already present to help compiling
	. take netbsd dirent.h and struct dirent; main result is
	  introducing d_type and d_namlen that have to be set by getdents()
	  in all FS code implementing it
	. d_off is gone
	. alignment of the struct has become 8 bytes instead of 4
	. remove _MAX_BLOCK_SIZE, _MIN_BLOCK_SIZE, _STATIC_BLOCK_SIZE
	. libminlib: cleanup unused yet duplicate code
	. mfs: throw out the long-broken v1, v2 support
	. new test for dirent contents filled by getdents()

Change-Id: I1459755c7ba5e5d1c9396d3a587ce6e63ddc283e

lib/libpuffs/subr.c

@@ -85,9 +85,6 @@ puffs_nextdent(struct dirent **dent, const char *name, ino_t id, uint8_t dtype,
 	if (o != 0)
 		reclen += sizeof(long) - o;
 
-        /* FIXME: Set d_off?
-         * dep->d_off = 
-         */
 	d->d_reclen = (unsigned short) reclen;
         (void)memcpy(d->d_name, name, (size_t)len);
         d->d_name[len] = '\0';