Fix issue with multiline captions not being wrapped in text versions

While working on my current PPing project I ran into an issue where long lines within a multiline caption were not being wrapped in the text versions. I'm not sure if this behavior was intentional, but I can't think of a case where wrapping here would be an issue. This change adds line wrap to multiline captions. 

Below is the ppgen code that illustrates the problem:
```
.il id=i141 fn=i_141.jpg w=62% alt='' 
.ca
<i>Fig. 14.</i>

<sc>Plant of Crosswort</sc> (<i><lang="la">Galium cruciatum</i>), with the larva and perfect insect of the <sc>Bloody-Nosed Beetle</sc> (<i><lang="la">Timarcha tenebricosa</lang></i>).
.ca-
```