title: unix timestamp round to midnight
body: <p>If I have a random unix timestamp, how can I round it down to today's midnight or the midnight selected by the user. The reason for this is that I want to add hours and minutes after a certain day's midnight.</p>
  
  <p>For example if the timestamp is <code>1324189035</code> then how can I remove the hours, minutes, and seconds to put the timestamp at midnight for that day.</p>