Stop occasionally making file systems with null UUIDs

mkfs.reiser4 was using strncpy() to copy a binary UUID into the
in-memory copy of the superblock.  So if there was a zero byte in the
UUID, then from that point to the end was set to all zeros.  If the
first byte was zero, a 1 in 256 chance, then the whole UUID was set to
zero generating a null UUID for the file system.  Fix this.

Test case:
    truncate -s 256M test.img
    i=0
    while :
    do
        mkfs.reiser4 --force --yes --label '' test.img
        line=`debugfs.reiser4 test.img 2> /dev/null | egrep '^uuid:'`
        ((i++))
        echo "[$i] $line"
        echo "$line" | grep -q '<none>' && break
    done

Output fragment:
    [1] uuid:               17073919-e41d-4892-9b22-4294d1544c4a
    [2] uuid:               af2821de-ea85-4f20-9621-4fbd128b3fb8
    [3] uuid:               c0fb805b-e224-4695-a504-d87460d158ae
    ...
    [34] uuid:              b747540d-5280-4e0f-bae2-922200000000
    [35] uuid:              d604794d-097f-4810-bbb3-01a1518f3ef1
    [36] uuid:              9634100c-1f98-42b3-a684-c9df77ab54e2
    [37] uuid:              <none>

Signed-off-by: Mike Fleetwood <mike.fleetwood@googlemail.com>

libreiser4/master.c

@@ -295,8 +295,8 @@ void reiser4_master_set_uuid(reiser4_master_t *master,
 		   sizeof(SUPER(master)->ms_uuid));
 
 	if (uuid) {
-		aal_strncpy(SUPER(master)->ms_uuid, uuid,
-			    sizeof(SUPER(master)->ms_uuid));
+		aal_memcpy(SUPER(master)->ms_uuid, uuid,
+			   sizeof(SUPER(master)->ms_uuid));
 	} 
 	master->dirty = 1;
 }