writing key to sys/{gold, nib, running} doesn't work correctly

doing the following shouldn't work (when 0.4.8000 is the loaded nib):

```echo "255.255.65535" > sys/nib/0.4.8000```

but it does.  SysNib.set_version(versionp) sees 0.4.8000 instead of 255.255.65535.

Bug on the tagfuse side.