Correct printing of strings in mixed error reports (reported by Bryan Hughes)

Since the lager_format rewrite, ~p and ~w now have different behaviour
with regard to printing lists as strings.

src/error_logger_lager_h.erl

@@ -266,9 +266,9 @@ print_silly_list([], Fmt, Acc) ->
     lager_trunc_io:format(string:join(lists:reverse(Fmt), ", "),
         lists:reverse(Acc), 4096);
 print_silly_list([{K,V}|T], Fmt, Acc) ->
-    print_silly_list(T, ["~w: ~w" | Fmt], [V, K | Acc]);
+    print_silly_list(T, ["~p: ~p" | Fmt], [V, K | Acc]);
 print_silly_list([H|T], Fmt, Acc) ->
-    print_silly_list(T, ["~w" | Fmt], [H | Acc]).
+    print_silly_list(T, ["~p" | Fmt], [H | Acc]).
 
 print_val(Val) ->
     {Str, _} = lager_trunc_io:print(Val, 500),

test/lager_test_backend.erl

@@ -509,7 +509,15 @@ error_logger_redirect_test_() ->
                         ?assert(length(lists:flatten(Msg)) < 5100)
                 end
             },
-
+            {"strings in a mixed report are printed as strings",
+                fun() ->
+                        sync_error_logger:info_report(["this is less silly", {than, "this"}]),
+                        _ = gen_event:which_handlers(error_logger),
+                        {_, _, Msg} = pop(),
+                        Expected = lists:flatten(io_lib:format("[info] ~w \"this is less silly\", than: \"this\"", [self()])),
+                        ?assertEqual(Expected, lists:flatten(Msg))
+                end
+            },
             {"info messages are printed",
                 fun() ->
                         sync_error_logger:info_msg("doom, doom has come upon you all"),