all: single space after period.

The tree's pretty inconsistent about single space vs double space
after a period in documentation. Make it consistently a single space,
per earlier decisions. This means contributors won't be confused by
misleading precedence.

This CL doesn't use go/doc to parse. It only addresses // comments.
It was generated with:

$ perl -i -npe 's,^(\s*// .+[a-z]\.)  +([A-Z]),$1 $2,' $(git grep -l -E '^\s*//(.+\.)  +([A-Z])')
$ go test go/doc -update

Change-Id: Iccdb99c37c797ef1f804a94b22ba5ee4b500c4f7
Reviewed-on: https://go-review.googlesource.com/20022
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Dave Day <djd@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/crypto/tls/handshake_server_test.go

@@ -69,7 +69,7 @@ func testClientHello(t *testing.T, serverConfig *Config, m handshakeMessage) {
 
 func testClientHelloFailure(t *testing.T, serverConfig *Config, m handshakeMessage, expectedSubStr string) {
 	// Create in-memory network connection,
-	// send message to server.  Should return
+	// send message to server. Should return
 	// expected error.
 	c, s := net.Pipe()
 	go func() {