Fix what appears to be a very old bug.  Tkinter in struni is more intolerant
of non-existant text widget 'marks', it seems.
diff --git a/Lib/idlelib/PyShell.py b/Lib/idlelib/PyShell.py
index 90c837c..bfd659c 100644
--- a/Lib/idlelib/PyShell.py
+++ b/Lib/idlelib/PyShell.py
@@ -961,6 +961,7 @@
     """
 
     def begin(self):
+        self.text.mark_set("iomark", "insert")
         self.resetoutput()
         if use_subprocess:
             nosub = ''