title: curl won't download empty file
body: <pre><code>curl -o foo.txt http://test.barrycarter.info/emptyfile.txt
  curl -O http://test.barrycarter.info/emptyfile.txt</code></pre>
  
  <p>I just tried both the above, and neither foo.txt nor emptyfile.txt were created.</p>
  
  <p>How can I make curl create them? Knowing that a file (URL) exists and is empty can be useful.</p>
  
  <p>In particular, I'm trying to mirror geonames daily updates, and it so happens that today's "<a href="http://download.geonames.org/export/dump/alternateNamesDeletes-2015-05-28.txt" rel="nofollow">http://download.geonames.org/export/dump/alternateNamesDeletes-2015-05-28.txt</a>" file is empty. It would be useful to know this instead of simply not downloading it.</p>
  
  <p>(Note: I created an emptyfile above for testing, since geonames' file will disappear within a day)</p>