Started to work on Python 3 support.

--HG--
branch : trunk
diff --git a/jinja2/tests.py b/jinja2/tests.py
index 58dc0c0..9fbf163 100644
--- a/jinja2/tests.py
+++ b/jinja2/tests.py
@@ -16,6 +16,13 @@
 regex_type = type(number_re)
 
 
+try:
+    test_callable = callable
+except NameError:
+    def test_callable(x):
+        return hasattr(x, '__call__')
+
+
 def test_odd(value):
     """Return true if the variable is odd."""
     return value % 2 == 1
@@ -130,7 +137,7 @@
     'number':           test_number,
     'sequence':         test_sequence,
     'iterable':         test_iterable,
-    'callable':         callable,
+    'callable':         test_callable,
     'sameas':           test_sameas,
     'escaped':          test_escaped
 }