fixed typo in gluon tools

VERSION

@@ -1 +1 @@
-Version 1.99.7 (2012-04-12 09:12:46) dev
+Version 1.99.7 (2012-04-15 09:55:17) dev

gluon/tools.py

@@ -1290,7 +1290,7 @@ class Auth(object):
         """
         tables = [table for table in tables]
         for table in tables: 
-            if 'modifed_on' in table.fields():
+            if 'modified_on' in table.fields():
                 table._enable_record_versioning(
                     archive_db = archive_db,
                     archive_name = archive_names,