what I propose is rather than using exclude=None for excluding bads (which btw sounds like don't exclude any) write explicitly exclude='bads' so

```
raw = fiff.Raw('whatever.fif')
picks = pick_types(raw.info, meg=True, eeg=False, exclude='bads')
epochs = Epochs(raw, picks=picks)
```

in terms of deprecation strategy we coudl have

0.6 : exclude=None in function signature with warning "choose 'bads' or []"
0.7 : exclude switch to 'bads' by default

although I have not sure I want this as default for a function called pick types that should be pretty dum, simple, stupid :)
btw MNE keeps the bads in average but ignores them, but for me doing epochs.get_data() and get only clean data is
pretty convenient.