This commit changes the application's reporting of elapsed time to
measure user time rather than wall time in order to reduce sources
of noise in evaluating runtime.

For output is now of the form:

  ```
  Processing time (wall): 123.456 s
  Processing time (user): 123.456 s
  ```



git-svn-id: http://wg11.sc29.org/svn/repos/MPEG-I/Part5-PointCloudCompression/TM/TMC3/trunk@1329 94298a81-5874-47c9-aab8-bfb24faeed7f