Revert r63934 -- it was mixing two patches.
diff --git a/PCbuild/rt.bat b/PCbuild/rt.bat
index 1ce0107..583d4f3 100644
--- a/PCbuild/rt.bat
+++ b/PCbuild/rt.bat
@@ -40,7 +40,7 @@
 
 PATH %PATH%;..\..\%tcltk%\bin
 set exe=%prefix%\python%suffix%
-set cmd=%exe% %dashO% -E ../lib/test/regrtest.py %1 %2 %3 %4 %5 %6 %7 %8 %9
+set cmd=%exe% %dashO% -E -tt ../lib/test/regrtest.py %1 %2 %3 %4 %5 %6 %7 %8 %9
 if defined qmode goto Qmode
 
 echo Deleting .pyc/.pyo files ...