Fix issues with the os module.

Using a try/finally assures that the recursion checkers work the right way.

test/test_api/test_api_classes.py

@@ -267,3 +267,14 @@ class TestGotoAssignments(TestCase):
         n = nms[1].goto_assignments()[0]
         assert n.name == 'load'
         assert n.type == 'function'
+
+        nms = names('import os; os.path', references=True)
+        assert nms[0].name == 'os'
+        assert nms[0].type == 'import'
+        n = nms[0].goto_assignments()[0]
+        assert n.name == 'os'
+        assert n.type == 'module'
+
+        n = nms[2].goto_assignments()[0]
+        assert n.name == 'path'
+        assert n.type == 'import'