Add setting to turn off diagonal correction for InducingPointKernel.

Author: AustinT

test/kernels/test_inducing_point_kernel.py

@@ -50,10 +50,12 @@ def test_kernel_output(self):
             self.assertTrue(ps_mock.called)
 
         # Check whether changing diagonal correction makes a difference (ensuring that cache is cleared)
-        model.train(); model.eval();
+        model.train()
+        model.eval()
         with gpytorch.settings.sgpr_diagonal_correction(True), torch.no_grad():
             output_mean_correct = model(test_x).mean
-        model.train(); model.eval();
+        model.train()
+        model.eval()
         with gpytorch.settings.sgpr_diagonal_correction(False), torch.no_grad():
             output_mean_no_correct = model(test_x).mean
         self.assertNotAlmostEqual(output_mean_correct.sum().item(), output_mean_no_correct.sum().item())