Input width in fluid rows

Created by: erquhart

When using a column-based width for an input inside of a div with class row-fluid, such as

<div class="row-fluid">
  <input class="span4">

and collapsing down to a tablet or phone-sized browser window, the input field defaults to width:auto, which is really small and static, regardless of which span width was indicated. If you change the code to

<div class="row">
  <input class="span4">

the input expands to 100% width on smaller screens, as it should, and as it does on Twitter Bootstrap's docs.