run-tests: work around the rename of xrange to range

tests/run-tests.py

@@ -76,6 +76,9 b' except ImportError:'
 
 processlock = threading.Lock()
 
+if sys.version_info > (3, 0, 0):
+    xrange = range # we use xrange in one place, and we'd rather not use range
+
 # subprocess._cleanup can race with any Popen.wait or Popen.poll on py24
 # http://bugs.python.org/issue1731717 for details. We shouldn't be producing
 # zombies but it's pretty harmless even if we do.