daysBefore[12+1]: index out of range time.December and Windows SYSTEMTIME.wMonth are 12 for December. R=rsc, dsymonds CC=golang-dev https://golang.org/cl/5448130
R=r, bradfitz, gri, dsymonds, iant CC=golang-dev https://golang.org/cl/5392041
Factor out sleep interrupt. Fixes #1109. R=alex.brainman, go.peter.90, mattn.jp CC=golang-dev https://golang.org/cl/4968041