Switch to glog for logging, bridge logging to glog.

1) imported glog to third_party (previous commit)
2) add support for third_party/update.sh to update just one pkg
3) search-and-replace:
  s/log.Printf/glog.Infof/
  s/log.Print/glog.Info/
  s/log.Fatalf/glog.Fatalf/
  s/log.Fatal/glog.Fatal/
4) convert glog.Info.*, err into glog.Error*

Adds some util interfaces to logging and calls them from each cmd, which
will set the default log output to write to glog.  Pass glog-wrapped
Loggers to etcd for logging.

Log files will go to /tmp - we should probably follow this up with a
default log dir for each cmd.

The glog lib is sort of weak in that it only flushes every 30 seconds, so
we spin up our own flushing goroutine.

pkg/util/logs.go

@@ -0,0 +1,50 @@
+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package util
+
+import (
+	"flag"
+	"log"
+	"time"
+
+	"github.com/golang/glog"
+)
+
+var logFlushFreq = flag.Duration("log_flush_frequency", 5*time.Second, "Maximum number of seconds between log flushes")
+
+// This serves as a bridge between the standard log package and the glog package.
+type GlogWriter struct{}
+
+func (writer GlogWriter) Write(data []byte) (n int, err error) {
+	glog.Info(string(data))
+	return len(data), nil
+}
+
+func InitLogs() {
+	log.SetOutput(GlogWriter{})
+	log.SetFlags(0)
+	// The default glog flush interval is 30 seconds, which is frighteningly long.
+	go Forever(glog.Flush, *logFlushFreq)
+}
+
+func FlushLogs() {
+	glog.Flush()
+}
+
+func NewLogger(prefix string) *log.Logger {
+	return log.New(GlogWriter{}, prefix, 0)
+}