Fixed #11776 -- Added CSS class for non-field/top of form errors.

Thanks Daniel Pope for the suggestion.

django/forms/utils.py

@@ -80,6 +80,14 @@ class ErrorList(UserList, list):
     """
     A collection of errors that knows how to display itself in various formats.
     """
+    def __init__(self, initlist=None, error_class=None):
+        super(ErrorList, self).__init__(initlist)
+
+        if error_class is None:
+            self.error_class = 'errorlist'
+        else:
+            self.error_class = 'errorlist {}'.format(error_class)
+
     def as_data(self):
         return ValidationError(self.data).error_list
 
@@ -99,8 +107,10 @@ class ErrorList(UserList, list):
     def as_ul(self):
         if not self.data:
             return ''
+
         return format_html(
-            '<ul class="errorlist">{0}</ul>',
+            '<ul class="{0}">{1}</ul>',
+            self.error_class,
             format_html_join('', '<li>{0}</li>', ((force_text(e),) for e in self))
         )