Abbreviations are destroyed by line breaks

Input:

``` markdown
*[foo bar]: baz

hello foo bar babble.

hello foo
bar babble.
```

Output:

``` html
<p>hello <abbr title="baz">foo bar</abbr> babble.</p>

<p>hello foo
bar babble.</p>
```

This is bad if the markdown author uses a line-breaking editor.
