added missing docs

doc/functions/block.rst

@@ -1,6 +1,9 @@
 ``block``
 =========
 
+.. versionadded: 1.28
+    Using ``block`` with the ``defined`` test was added in Twig 1.28.
+ 
 When a template uses inheritance and if you want to print a block multiple
 times, use the ``block`` function:
 

doc/functions/constant.rst

@@ -4,6 +4,9 @@
 .. versionadded: 1.12.1
     constant now accepts object instances as the second argument.
 
+.. versionadded: 1.28
+    Using ``constant`` with the ``defined`` test was added in Twig 1.28.
+
 ``constant`` returns the constant value for a given string:
 
 .. code-block:: jinja