Multiple multiline strings were not being reformatted correct.

Code that had one multiline string was handled correctly. However, if
there were multiple multiline strings for a line of code, it wouldn't
format them correctly. E.g.:

```
def f():
    email_text += """<html>This is a really long docstring that goes
over the column limit and is multi-line.<br><br>
<b>Czar: </b>"""+despot["Nicholas"]+"""<br>
<b>Minion: </b>"""+serf["Dmitri"]+"""<br>
<b>Residence: </b>"""+palace["Winter"]+"""<br>
</body>
</html>"""
```

is formatted to this:

```
def f():
    email_text += """<html>This is a really long docstring that goes over the column limit and is multi-line.<br><br>
<b>Czar: </b>""" + despot["Nicholas"] + """<br>
<b>Minio
        n: </b>
        """ + serf["Dmitri"] + """<br>
<b>Residence: </b>""" + palace["Winter"] + """<br>
</body>
</html>"""
```

This patch takes the bit where it's taking multiline offsets into
account and makes it more general.