Found and fixed the source of the "AttributeError: __error_log__" bug.

This code looks for the __error_log__ attribute in order to report an
error.  If it finds no such attribute, it reports the error in a
different way.  Unfortunately, the alternative branch was reporting
the exception that just happened to occur most recently, which is
irrelevant; it needs to report the error that was passed to it.
Fixed.

lib/python/Zope/App/startup.py

@@ -184,7 +184,8 @@ def zpublisher_exception_hook(published, REQUEST, t, v, traceback):
             f=getattr(published, 'raise_standardErrorMessage', None)
             if f is None:
                 published=getattr(published, 'aq_parent', None)
-                if published is None: raise
+                if published is None:
+                    raise t, v, traceback
             else:
                 break
 
@@ -193,7 +194,8 @@ def zpublisher_exception_hook(published, REQUEST, t, v, traceback):
             if getattr(client, 'standard_error_message', None) is not None:
                 break
             client=getattr(client, 'aq_parent', None)
-            if client is None: raise
+            if client is None:
+                raise t, v, traceback
 
         if REQUEST.get('AUTHENTICATED_USER', None) is None:
             REQUEST['AUTHENTICATED_USER']=AccessControl.User.nobody