python: setup the dependent environment properly

We want the run dependencies of all build and run dependencies of the
current package.

var/spack/repos/builtin/packages/python/package.py

@@ -146,7 +146,7 @@ def setup_dependent_environment(self, spack_env, run_env, extension_spec):
         extension and any other python extensions it depends on."""
 
         python_paths = []
-        for d in extension_spec.traverse():
+        for d in extension_spec.traverse(deptype=nolink, deptype_query='run'):
             if d.package.extends(self.spec):
                 python_paths.append(join_path(d.prefix,
                                               self.site_packages_dir))