[LIBXGBOOST] pass demo running.

demo/guide-python/runall.sh

@@ -1,4 +1,5 @@
 #!/bin/bash
+export PYTHONPATH=PYTHONPATH:../../python-package
 python basic_walkthrough.py
 python custom_objective.py
 python boost_from_prediction.py
@@ -9,4 +10,4 @@ python predict_leaf_indices.py
 python sklearn_examples.py
 python sklearn_parallel.py
 python external_memory.py
-rm -rf *~ *.model *.buffer 
+rm -rf *~ *.model *.buffer