title: NSDate for first day of the month
body: <p>This is quite a simple concept, but as of yet I have been unable to find an elegant (and calendar locale independent) solution. I need to find the first day of the month for an arbitrary <code>NSDate</code>. For example, given an arbitrary <code>NSDate</code> (<code>arbitraryDate</code>) another NSDate object will be returned (let's call this <code>firstDayOfMonthDate</code>) which represents the first day of the month in <code>arbitraryDate</code>. The time component does not matter, as I just need the NSDate object for the first day of the month (although for neatness it would be useful if the time was just zeroed out).</p>
  
  <p>Thanks in advance for any assistance.</p>