go/printer, gofmt: don't write too many newlines

In some rare cases, gofmt would accept more than the maximum
number of empty lines (1) between source code snippets.

The actual change is in printer.go, lines 773-775; the rest
is some minor restructuring.

Applied gofmt -w src misc .

Fixes #2387.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/5496047

src/pkg/bytes/buffer_test.go

@@ -16,7 +16,6 @@ const N = 10000  // make this bigger for a larger (and slower) test
 var data string  // test data for write tests
 var bytes []byte // test data; same as data but as a slice.
 
-
 func init() {
 	bytes = make([]byte, N)
 	for i := 0; i < N; i++ {