Merge pull request #484 from michelts/import_module_deprecation_warning

Avoid deprecation warning about django's importlib and prepare to django 1.9.

lettuce/django/apps.py

@@ -16,7 +16,10 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 from os.path import join, dirname
-from django.utils.importlib import import_module
+try:
+    from importlib import import_module
+except ImportError:
+    from django.utils.importlib import import_module
 from django.conf import settings