Show deprecation warning only after using A() queries

Author: aburgel

django_mongodb_engine/query.py

@@ -1,7 +1,4 @@
 from warnings import warn
-warn("A() queries are deprecated as of 0.5 and will be removed in 0.6.",
-     DeprecationWarning)
-
 
 from djangotoolbox.fields import RawField, AbstractIterableField, \
     EmbeddedModelField
@@ -16,6 +13,8 @@
 class A(object):
 
     def __init__(self, op, value):
+        warn("A() queries are deprecated as of 0.5 and will be removed in 0.6.", DeprecationWarning) 
+
         self.op = op
         self.val = value