Fix duplicated items in bs-popover with ng-repeat

For some reason, bootstrap is calling the content() function twice. This
doesn't necessarily produce any ill effects, but if your bs-popover
partial contained an ng-repeat, the ng-repeat would be replicated once
for every element in the collection.

For example, this:

```
 $scope.things = [{name: "A"}, {name: "B"}, {name: "C"}];

 <ul>
   <li ng-repeat="thing in things">{{thing.name}}</li>
  </ul>
```

Would yield a popover that appeared like this:

    - A
    - A
    - A
    - B
    - B
    - B
    - C
    - C
    - C

But it should have appeared like this:

    - A
    - B
    - C