Unintuitive PROTECT length

This errors:
```
PROTECT $E842 
ORG $e845 
BYTE 1 
```

while this does not:

```
PROTECT $E842 $E843
ORG $e845 
BYTE 1 
```

I believe `PROTECT` when used without an end address given assumes a length of 4 bytes. If it's easy to do, I think it should protect until the next 4-alignment instead. 
