penReg problem when penalty is scaled bug

This is related to the mgcv issue 

https://github.com/mfasiolo/mgcv/issues/24

Here a new version of penReg solves it:

5880d9e0726c8e3c94e419163810d60a887f482b

BUT the way we calculate the rank of the penalty:

```
rp <- Rrank(qr.R(qr(e)))
```

is probably not good.