IS_EXPR_environment.patch, fixed issue 938, thanks Anthony

VERSION

@@ -1 +1 @@
-Version 2.00.0 (2012-08-18 20:11:01) dev
+Version 2.00.0 (2012-08-19 10:02:26) dev

gluon/validators.py

@@ -213,14 +213,15 @@ class IS_EXPR(Validator):
         ('2', 'invalid expression')
     """
 
-    def __init__(self, expression, error_message='invalid expression'):
+    def __init__(self, expression, error_message='invalid expression', environment=None):
         self.expression = expression
         self.error_message = error_message
+        self.environment = environment or {}
 
     def __call__(self, value):
-        environment = {'value': value}
-        exec '__ret__=' + self.expression in environment
-        if environment['__ret__']:
+        self.environment.update(value=value)
+        exec '__ret__=' + self.expression in self.environment
+        if self.environment['__ret__']:
             return (value, None)
         return (value, translate(self.error_message))