Put repeated elements next to their friends instead of at the end of the parent

I wanted to repeat an element that was in between others:

```
  <div>
    <p>Introductory text</p>
    <p meld:id="repeatme">Replace me</p>
    <p>Parting text</p>
  </div>
```

However the repeated elements are inserted after "Parting text" because repeat() does an append.

This patch attempts to insert next to the parent, so that the example works. I'm slightly nervous that it changes existing behaviour, but I would guess that it's unlikely people would rely on it appending after the fixed elements?