crypto/ssh: Allow customization of the client version.

R=agl, golang-dev, dave
CC=golang-dev
https://golang.org/cl/13176044

ssh/client_test.go

@@ -0,0 +1,34 @@
+package ssh
+
+import (
+	"net"
+	"testing"
+)
+
+func testClientVersion(t *testing.T, config *ClientConfig, expected string) {
+	clientConn, serverConn := net.Pipe()
+	receivedVersion := make(chan string, 1)
+	go func() {
+		version, err := readVersion(serverConn)
+		if err != nil {
+			receivedVersion <- ""
+		} else {
+			receivedVersion <- string(version)
+		}
+		serverConn.Close()
+	}()
+	Client(clientConn, config)
+	actual := <-receivedVersion
+	if actual != expected {
+		t.Fatalf("got %s; want %s", actual, expected)
+	}
+}
+
+func TestCustomClientVersion(t *testing.T) {
+	version := "Test-Client-Version-0.0"
+	testClientVersion(t, &ClientConfig{ClientVersion: version}, version)
+}
+
+func TestDefaultClientVersion(t *testing.T) {
+	testClientVersion(t, &ClientConfig{}, string(clientVersion))
+}