loopback example: log microsecond timestamps

Seconds granularity is too coarse to understand what is
happening, so add microseconds. In return, the date
is dropped to keep the lines short.

Old format:
  2016/03/14 18:19:38 Dispatch: OPENDIR, NodeId: 1.

New format:
  18:18:35.988071 Dispatch: OPENDIR, NodeId: 1.

example/loopback/main.go

@@ -4,6 +4,7 @@
 package main
 
 import (
+	"log"
 	"flag"
 	"fmt"
 	"os"
@@ -18,6 +19,7 @@ import (
 )
 
 func main() {
+	log.SetFlags(log.Lmicroseconds)
 	// Scans the arg list and sets up flags
 	debug := flag.Bool("debug", false, "print debugging messages.")
 	other := flag.Bool("allow-other", false, "mount with -o allowother.")