net, io/ioutil: remove use of os.Time

I had to replace the single use of io/ioutil
in the time package with a bytes.Buffer since
there would've been a dependency cycle.

There are no other uses of os.Time.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5372054

src/pkg/io/ioutil/tempfile.go

@@ -8,6 +8,7 @@ import (
 	"os"
 	"path/filepath"
 	"strconv"
+	"time"
 )
 
 // Random number state, accessed without lock; racy but harmless.
@@ -17,8 +18,7 @@ import (
 var rand uint32
 
 func reseed() uint32 {
-	sec, nsec, _ := os.Time()
-	return uint32(sec*1e9 + nsec + int64(os.Getpid()))
+	return uint32(time.Nanoseconds() + int64(os.Getpid()))
 }
 
 func nextSuffix() string {

src/pkg/net/hosts.go

@@ -7,8 +7,8 @@
 package net
 
 import (
-	"os"
 	"sync"
+	"time"
 )
 
 const cacheMaxAge = int64(300) // 5 minutes.
@@ -26,7 +26,7 @@ var hosts struct {
 }
 
 func readHosts() {
-	now, _, _ := os.Time()
+	now := time.Seconds()
 	hp := hostsPath
 	if len(hosts.byName) == 0 || hosts.time+cacheMaxAge <= now || hosts.path != hp {
 		hs := make(map[string][]string)
@@ -51,7 +51,7 @@ func readHosts() {
 			}
 		}
 		// Update the data cache.
-		hosts.time, _, _ = os.Time()
+		hosts.time = time.Seconds()
 		hosts.path = hp
 		hosts.byName = hs
 		hosts.byAddr = is

src/pkg/time/zoneinfo_unix.go

@@ -12,7 +12,7 @@
 package time
 
 import (
-	"io/ioutil"
+	"bytes"
 	"os"
 )
 
@@ -180,11 +180,17 @@ func parseinfo(bytes []byte) (zt []zonetime, ok bool) {
 }
 
 func readinfofile(name string) ([]zonetime, bool) {
-	buf, err := ioutil.ReadFile(name)
+	var b bytes.Buffer
+
+	f, err := os.Open(name)
 	if err != nil {
 		return nil, false
 	}
-	return parseinfo(buf)
+	defer f.Close()
+	if _, err := b.ReadFrom(f); err != nil {
+		return nil, false
+	}
+	return parseinfo(b.Bytes())
 }
 
 func setupTestingZone() {