add __pycache__ to clean-pyc target of Makefile

Author: oesteban

Makefile

@@ -32,6 +32,7 @@ trailing-spaces:
 
 clean-pyc:
 	find . -name "*.pyc" | xargs rm -f
+	find . -name "__pycache__" -type d | xargs rm -rf
 
 clean-so:
 	find . -name "*.so" | xargs rm -f