Fix Python 2 issues

doc/test_inference.py

@@ -4,6 +4,9 @@ from __future__ import print_function
 
 verbose=False
 
+if __name__ == "__main__":
+    verbose = True
+
 import os
 import sys
 if not verbose:

src/graph_tool/inference/layered_blockmodel.py

@@ -47,7 +47,7 @@ from . blockmodel import *
 from . blockmodel import _bm_test
 from . overlap_blockmodel import *
 
-class LayeredBlockState(BlockState):
+class LayeredBlockState(OverlapBlockState, BlockState):
     r"""The (possibly overlapping) block state of a given graph, where the edges are
     divided into discrete layers.