resolved clang compiler errors for test_dualdecomposition

Error message below:

```
/Users/nonadmin/local/tmp/opengm/src/unittest/inference/test_dualdecomposition.cxx:49:14: error: use 'template' keyword to treat 'test' as a dependent template name
      tester.test<DualDecompositionType>(para);  
             ^
             template 
/Users/nonadmin/local/tmp/opengm/src/unittest/inference/test_dualdecomposition.cxx:55:14: error: use 'template' keyword to treat 'test' as a dependent template name
      tester.test<DualDecompositionType>(para);
             ^
             template 
```