title: Colon (:) appears as forward slash (/) when creating file name
body: <p>I am using date and time to label a new file that I'm creating, but when I view the file, the colon is a forward slash. I am developing on a Mac using 10.7+</p>
  
  <p>Here is the code I'm using: </p>
  
  <pre><code> File.open("#{time.hour} : 00, #{time.month}-#{time.day}-#{time.year}", "a") do |mFile|
          mFile.syswrite("#{pKey} - #{tKey}: \n") 
          mFile.syswrite("Items closed: #{itemsClosed} | Total items: #{totalItems} | Percent closed: % #{pClosed} \n") 
          mFile.syswrite("\n")
          mFile.close
       end
  </code></pre>
  
  <p>Here is the output (assuming the time is 1pm):</p>
  
  <pre><code>13 / 00, 11-8-2012
  </code></pre>
  
  <p>Why is this happening and how can I fix it? I want the output to be:</p>
  
  <pre><code>13:00, 11-8-2012
  </code></pre>