delete-dir-force gives bad suggestion if space in filename

The delete-dir-force alias should quote filenames in suggestions:

```
$ ls foo\ bar/
it.txt

$ delete-dir-force 'foo bar'
Warning: run enable-forced-deletions or issue: command rm -rfv foo bar

$ rm -rfv foo bar

$ ls -R
.:
'foo bar'

'./foo bar':
it.txt
```