fixed some NameErrors

--HG--
branch : trunk
diff --git a/jinja2/exceptions.py b/jinja2/exceptions.py
index 0bbe33e..b0853c4 100644
--- a/jinja2/exceptions.py
+++ b/jinja2/exceptions.py
@@ -45,3 +45,9 @@
 
 class TemplateRuntimeError(TemplateError):
     """A runtime error."""
+
+
+class FilterArgumentError(Exception):
+    """This error is raised if a filter was called with inappropriate
+    arguments
+    """