crypto/tls: note in comments that setting GetCertificate is now sufficient.

In Go 1.5, Config.Certificates is no longer required if
Config.GetCertificate has been set. This change updated four comments to
reflect that.

Change-Id: Id72cc22fc79e931b2d645a7c3960c3241042762c
Reviewed-on: https://go-review.googlesource.com/13800
Reviewed-by: Adam Langley <agl@golang.org>

src/crypto/tls/tls.go

diff --git a/src/crypto/tls/tls.go b/src/crypto/tls/tls.go
index f6d5bb1..fb399d0 100644
--- a/src/crypto/tls/tls.go
+++ b/src/crypto/tls/tls.go
@@ -20,8 +20,8 @@
 
 // Server returns a new TLS server side connection
 // using conn as the underlying transport.
-// The configuration config must be non-nil and must have
-// at least one certificate.
+// The configuration config must be non-nil and must include
+// at least one certificate or else set GetCertificate.
 func Server(conn net.Conn, config *Config) *Conn {
 	return &Conn{conn: conn, config: config}
 }
@@ -53,8 +53,8 @@
 
 // NewListener creates a Listener which accepts connections from an inner
 // Listener and wraps each connection with Server.
-// The configuration config must be non-nil and must have
-// at least one certificate.
+// The configuration config must be non-nil and must include
+// at least one certificate or else set GetCertificate.
 func NewListener(inner net.Listener, config *Config) net.Listener {
 	l := new(listener)
 	l.Listener = inner
@@ -64,8 +64,8 @@
 
 // Listen creates a TLS listener accepting connections on the
 // given network address using net.Listen.
-// The configuration config must be non-nil and must have
-// at least one certificate.
+// The configuration config must be non-nil and must include
+// at least one certificate or else set GetCertificate.
 func Listen(network, laddr string, config *Config) (net.Listener, error) {
 	if config == nil || (len(config.Certificates) == 0 && config.GetCertificate == nil) {
 		return nil, errors.New("tls: neither Certificates nor GetCertificate set in Config")