Add back some implicit imports where needed

- I took a gamble on how far we can go, now need to remedy
4 jobs for 111-explicit-relative in 1 minute and 38 seconds
Status Name Job ID Coverage
  Test
passed Go-py2.7 #2641

00:01:35

passed Go-py3.4 #2642

00:01:38

passed Go-py3.5 #2643

00:01:37

passed Go-py3.6 #2644

00:01:34