Support dry runs in SimpleTest, as well as misc other improvements.

git-svn-id: http://htmlpurifier.org/svnroot/htmlpurifier/trunk@1514 48356398-32a2-884e-a903-53898d9a118a

tests/index.php

@@ -10,6 +10,7 @@
  *   - standalone, whether or not to test the standalone version
  *   - file (f), a single file to test
  *   - xml, whether or not to output XML
+ *   - dry, whether or not to do a dry run
  */
 
 define('HTMLPurifierTest', 1);