Use render function will be strange when `\n` in slot template.

### Vue.js version
2.0.6

### Reproduction Link
https://jsfiddle.net/yu2h7utk/

### Steps to reproduce / What is actually happening?
- The different in A, B, C, D buttons is `\n` between two DOM node.
- Click A, B, C, D button，only D button will be normal, others will duplice the text