Merge branch '3.x' into 4.x

* 3.x:
  Tweak null-safe operator implementation
  Add null-safe operator
  Update u.rst to clarify truncate method's third argument behavior

Author: fabpot

Tests/Fixtures/script_names.test

@@ -2,15 +2,15 @@
 "script_names" function
 --TEMPLATE--
 {{ script_names('UNKNOWN')|length }}
-{{ script_names() is iterable }}
-{{ script_names('fr') is iterable }}
+{{ script_names()|length > 200 ? 'more than 200' : 'less than 200' }}
+{{ script_names('fr')|length > 200 ? 'more than 200' : 'less than 200' }}
 {{ script_names()['Marc'] }}
 {{ script_names('fr')['Marc'] }}
 --DATA--
 return [];
 --EXPECT--
 0
-1
-1
+more than 200
+more than 200
 Marchen
 Marchen