x/crypto/otr: make errors fatal.

Since the test against libotr (disabled by default) runs forever, any
errors should be fatal otherwise they'll never be noticed.

Change-Id: Idf07dd963260f140be1950afcbd04331b56bd627
Reviewed-on: https://go-review.googlesource.com/16935
Reviewed-by: Andrew Gerrand <adg@golang.org>

otr/otr_test.go

@@ -450,7 +450,7 @@ func TestAgainstLibOTR(t *testing.T) {
 		if change == NewKeys {
 			alicesMessage, err := alice.Send([]byte("Go -> libotr test message"))
 			if err != nil {
-				t.Errorf("error sending message: %s", err.Error())
+				t.Fatalf("error sending message: %s", err.Error())
 			} else {
 				for _, msg := range alicesMessage {
 					out.Write(msg)
@@ -460,10 +460,10 @@ func TestAgainstLibOTR(t *testing.T) {
 		}
 		if len(text) > 0 {
 			if !bytes.Equal(text, expectedText) {
-				t.Errorf("expected %x, but got %x", expectedText, text)
+				t.Fatalf("expected %x, but got %x", expectedText, text)
 			}
 			if !encrypted {
-				t.Error("message wasn't encrypted")
+				t.Fatal("message wasn't encrypted")
 			}
 		}
 	}