title: Check whether a string is a valid filename with Qt
body: <p>Is there a way with <code>Qt 4.6</code> to check if a given <code>QString</code> is a valid filename (or directory name) on the current operating system ? I want to check for the name to be valid, <em>not</em> for the file to exist.</p>
  
  <p>Examples:</p>
  
  <pre><code>// Some valid names
  test
  under_score
  .dotted-name
  
  // Some specific names
  colon:name // valid under UNIX OSes, but not on Windows
  what? // valid under UNIX OSes, but still not on Windows
  </code></pre>
  
  <p>How would I achieve this ? Is there some <code>Qt</code> built-in function ?</p>
  
  <p>I'd like to avoid creating an empty file, but if there is no other reliable way, I would still like to see how to do it in a "clean" way.</p>
  
  <p>Many thanks.</p>