fixed db(((db.table1.field1 + db.table1.field2)>4)).select(), thanks Boris

VERSION

@@ -1 +1 @@
-Version 2.8.2-stable+timestamp.2013.12.09.21.27.36
+Version 2.8.2-stable+timestamp.2013.12.11.20.32.28

gluon/dal.py

@@ -1460,7 +1460,7 @@ class BaseAdapter(ConnectionPool):
         return '(%s)' % ' || '.join(self.expand(x,'string') for x in items)
 
     def ADD(self, first, second):
-        if self.is_numerical_type(first.type):
+        if self.is_numerical_type(first.type) or isinstance(first.type, gluon.dal.Field):
             return '(%s + %s)' % (self.expand(first),
                                   self.expand(second, first.type))
         else: