crypto/tls: support TLS 1.1.

The significant change between TLS 1.0 and 1.1 is the addition of an explicit IV in the case of CBC encrypted records. Support for TLS 1.1 is needed in order to support TLS 1.2.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/7880043
diff --git a/src/pkg/crypto/tls/handshake_server.go b/src/pkg/crypto/tls/handshake_server.go
index 6c40489..0c96a2b 100644
--- a/src/pkg/crypto/tls/handshake_server.go
+++ b/src/pkg/crypto/tls/handshake_server.go
@@ -98,7 +98,7 @@
 	if !ok {
 		return false, c.sendAlert(alertUnexpectedMessage)
 	}
-	c.vers, ok = mutualVersion(hs.clientHello.vers)
+	c.vers, ok = config.mutualVersion(hs.clientHello.vers)
 	if !ok {
 		return false, c.sendAlert(alertProtocolVersion)
 	}
@@ -203,7 +203,7 @@
 	if hs.sessionState.vers > hs.clientHello.vers {
 		return false
 	}
-	if vers, ok := mutualVersion(hs.sessionState.vers); !ok || vers != hs.sessionState.vers {
+	if vers, ok := c.config.mutualVersion(hs.sessionState.vers); !ok || vers != hs.sessionState.vers {
 		return false
 	}