title: need better method to check swf version to avoid cache (not flash player version)
body: <p><strong>Why we have this problem</strong><br>
  swf file generated by Flash will be cached by web browser.<br>
  there're hundreds of swfs in our project, and we update the project every week.<br>
  with every update some swf files might be changed and we need to make sure every user will reload those newest files not cache.<br>
  we're having a method by recording versions of all files but that cost too much.<br>
  <strong>AND we don't want other unchanged files to be updated by users</strong> so timestamp way doesn't help.
  <br><br>
  <strong>now comes the question</strong><br>
  any better ideas? </p>