reverting r45321: Patch #860326: traceback.format_exception_only() now
prepends the exception's module name to non-builtin exceptions, like
the interpreter itself does.

broke a number of doctests. should be discussed before checking in (see
discussion on python-dev).
diff --git a/Lib/traceback.py b/Lib/traceback.py
index 56a87dc..454eb1b 100644
--- a/Lib/traceback.py
+++ b/Lib/traceback.py
@@ -158,12 +158,8 @@
     """
     list = []
     if (type(etype) == types.ClassType
-        or (isinstance(etype, type) and issubclass(etype, BaseException))):
+        or (isinstance(etype, type) and issubclass(etype, Exception))):
         stype = etype.__name__
-        if not hasattr(etype, '__module__'):
-            stype = '<unknown>.' + stype
-        elif etype.__module__ != 'exceptions':
-            stype = etype.__module__ + '.' + stype
     else:
         stype = etype
     if value is None: