mypy: add typeshed/2and3 in mypypath

Author: manu-chroma

Makefile

@@ -169,7 +169,7 @@ mypy: ${PYSOURCES}
 	rm -Rf typeshed/2.7/ruamel/yaml
 	ln -s $(shell python -c 'from __future__ import print_function; import ruamel.yaml; import os.path; print(os.path.dirname(ruamel.yaml.__file__))') \
 		typeshed/2.7/ruamel/
-	MYPYPATH=typeshed/2.7 mypy --py2 --disallow-untyped-calls \
+	MYPYPATH=$MYPYPATH:typeshed/2.7:typeshed/2and3 mypy --py2 --disallow-untyped-calls \
 		 --warn-redundant-casts --warn-unused-ignores \
 		 schema_salad