Make sure in setup.py that the typeshed submodule is loaded

setup.py

@@ -2,6 +2,7 @@
 
 from setuptools import setup, find_packages
 
+import os
 import ast
 
 __AUTHOR__ = 'David Halter'
@@ -16,6 +17,9 @@ readme = open('README.rst').read() + '\n\n' + open('CHANGELOG.rst').read()
 with open('requirements.txt') as f:
     install_requires = f.read().splitlines()
 
+assert os.path.isfile("third_party/typeshed/LICENSE"), \
+    "Please download the typeshed submodule first"
+
 setup(name='jedi',
       version=version,
       description='An autocompletion tool for Python that can be used for text editors.',