Properly stop the repo and revwalk servers

Return the 4-tuple when asked to stop instead of the 3-tuple so we do
indicate the stop was normal.

test/repo_test.erl

@@ -22,5 +22,5 @@ odb_write_test(Repo) ->
     Expected = geef_oid:parse("c300118399f01fe52b316061b5d32beb27e0adfd"),
     [?_assertEqual(Actual, Expected)].
 
-stop(_Repo) ->
-    ok.
+stop(Repo) ->
+    geef_repo:stop(Repo).

test/revwalk_test.erl

@@ -28,7 +28,9 @@ amount_test(Repo) ->
     {ok, Walk} = geef_repo:revwalk(Repo),
     Id = geef_oid:parse("a4a7dce85cf63874e984719f4fdd239f5145052f"),
     ok = geef_revwalk:push(Walk, Id),
-    [?_assertEqual(6, count_walk(Walk, 0))].
+    Count = count_walk(Walk, 0),
+    geef_revwalk:stop(Walk),
+    [?_assertEqual(6, Count)].
 
-stop(_Repo) ->
-    ok.
+stop(Repo) ->
+    geef_repo:stop(Repo).