Fill the line cache

The difference between 

```python
(Pdb) l
[EOF]
```

and


```python
(Pdb) l
 19
 20     allCasesAndReportsById = db.getView('allCasesAndReportsById')
 21     cases_and_reports = allCasesAndReportsById.getAllDocuments(getObject=False)
 22
 23     import pdb; pdb.set_trace()
 24  -> return ['%s|%s' % (b.PlominoViewColumn_allCasesAndReportsById_doctitle, b.id) for b in cases_and_reports]
```

I didn't actually realise I was only getting this because I had ``zdb`` hanging around.