title: txtProgressBar not updating on Mac R Console
body: <p>My R (3.0.2) console doesn't update a <code>txtProgressBar</code> until all the code has executed (defeating the purpose of a progress bar). I've been running the following:</p>
  
  <pre><code>pb &lt;- txtProgressBar(0, 20, 0)
  for (i in 1:20) {
      Sys.sleep(0.5)
      setTxtProgressBar(pb, i)
  }
  </code></pre>
  
  <p>Nothing is output for 10 seconds (the time to execute the whole code segment) and then the entire progress bar is printed out. This behavior doesn't change if I add a <code>flush.console()</code> call after the <code>setTxtProgressBar</code> call.</p>
  
  <p>I suspect this is Mac R console-specific, as the progress bar works as expected in the linux R console. How can I get the expected progress bar behavior?</p>