Addon missing left border when used inside form, inside a row

[Owen Versteeg]

From #67

First addon: correct
Second addon: missing left border

Code to reproduce:

<div class="container">
    <form class="row">
        <div>
            <span class="addon">$</span><input type="text" value="foo!" />
        </div>
    </form>
</div>

Currently an issue in Safari, FF, presumably all/most other browsers