doc: document that weekly.html is only a historical reference

Fixes issue 4810.

R=golang-dev, r
CC=golang-dev
https://codereview.appspot.com/7401050
time: handle very large sleep durations

Fixes issue 4903.

R=golang-dev, daniel.morsing, dave, r
CC=golang-dev
https://codereview.appspot.com/7388056