gofmt: simpler walkDir

Swapping the goroutines lets them reuse the
communication completion on v instead of
needing a second channel (done).

R=gri
CC=golang-dev
https://golang.org/cl/4287045

src/cmd/gofmt/gofmt.go

@@ -158,21 +158,16 @@ func (v fileVisitor) VisitFile(path string, f *os.FileInfo) {
 
 
 func walkDir(path string) {
-	// start an error handler
-	done := make(chan bool)
 	v := make(fileVisitor)
 	go func() {
-		for err := range v {
-			if err != nil {
-				report(err)
-			}
-		}
-		done <- true
+		filepath.Walk(path, v, v)
+		close(v)
 	}()
-	// walk the tree
-	filepath.Walk(path, v, v)
-	close(v) // terminate error handler loop
-	<-done   // wait for all errors to be reported
+	for err := range v {
+		if err != nil {
+			report(err)
+		}
+	}
 }