lib/time: add README, update.bash script

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/5674104

lib/time/README

+The zoneinfo directory contains time zone files compiled using
+the code and data maintained as part of the IANA Time Zone Database.
+The IANA asserts that the database is in the public domain.
+
+For more information, see
+http://www.iana.org/time-zones
+ftp://ftp.iana.org/tz/code/tz-link.htm
+http://tools.ietf.org/html/draft-lear-iana-timezone-database-05
+

lib/time/update.bash

+#!/bin/sh
+# Copyright 2012 The Go Authors.  All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file.
+
+# This script rebuilds the time zone files using files
+# downloaded from the ICANN/IANA distribution.
+
+# Versions to use.
+CODE=2011i
+DATA=2011n
+
+set -e
+rm -rf zoneinfo work
+mkdir zoneinfo work
+cd work
+curl -O http://www.iana.org/time-zones/repository/releases/tzcode$CODE.tar.gz
+curl -O http://www.iana.org/time-zones/repository/releases/tzdata$DATA.tar.gz
+tar xzf tzcode$CODE.tar.gz
+tar xzf tzdata$DATA.tar.gz
+
+# Turn off 64-bit output in time zone files.
+# We don't need those until 2037.
+perl -p -i -e 's/pass <= 2/pass <= 1/' zic.c
+
+make CFLAGS=-DSTD_INSPIRED AWK=awk TZDIR=../zoneinfo posix_only
+
+# America/Los_Angeles should not be bigger than 1100 bytes.
+# If it is, we probably failed to disable the 64-bit output, which
+# triples the size of the files.
+size=$(ls -l ../zoneinfo/America/Los_Angeles | awk '{print $5}')
+if [ $size -gt 1200 ]; then
+	echo 'zone file too large; 64-bit edit failed?' >&2
+	exit 2
+fi
+
+cd ..
+hg addremove zoneinfo
+echo
+if [ "$1" == "-work" ]; then 
+	echo Left workspace behind in work/.
+else
+	rm -rf work
+fi
+echo New time zone files in zoneinfo/.