Fixed #18785 -- Added Test join trimming regression

The regression was caused by patch to ticket #15316 and was fixed by a
patch to #10790.

tests/queries/tests.py

@@ -2852,3 +2852,14 @@ class DoubleInSubqueryTests(TestCase):
         qs = LeafB.objects.filter(pk__in=joins)
         self.assertQuerysetEqual(
             qs, [lfb1], lambda x: x)
+
+class Ticket18785Tests(unittest.TestCase):
+    def test_ticket_18785(self):
+        # Test join trimming from ticket18785
+        qs = Item.objects.exclude(
+            note__isnull=False
+        ).filter(
+            name='something', creator__extra__isnull=True
+        ).order_by()
+        self.assertEquals(1, str(qs.query).count('INNER JOIN'))
+        self.assertEquals(0, str(qs.query).count('OUTER JOIN'))