Allow for the possibility that globals['__name__'] does not exist;

substitute "<string>" for the module name in that case.  This actually
occurred when running test_descr.py with -Dwarn.

Lib/warnings.py

@@ -24,7 +24,10 @@ def warn(message, category=None, stacklevel=1):
     else:
         globals = caller.f_globals
         lineno = caller.f_lineno
+    if globals.has_key('__name__'):
         module = globals['__name__']
+    else:
+        module = "<string>"
     filename = globals.get('__file__')
     if filename:
         fnl = filename.lower()