Py3 fix: missing intern import

loopy/kernel/tools.py

 """Operations on the kernel object."""
 
-from __future__ import division
-from __future__ import absolute_import
-import six
+from __future__ import division, absolute_import
 
 __copyright__ = "Copyright (C) 2012 Andreas Kloeckner"
 
@@ -26,6 +24,8 @@ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 THE SOFTWARE.
 """
 
+import six
+from six.moves import intern
 
 import numpy as np
 from islpy import dim_type