Register spec types in client

Allow types to be registred multiple times instead of panic.

Fixes #1235

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

typeurl/types.go

@@ -26,7 +26,7 @@ func Register(v interface{}, args ...string) {
 	mu.Lock()
 	defer mu.Unlock()
 	if _, ok := registry[t]; ok {
-		panic(errdefs.ErrAlreadyExists)
+		return
 	}
 	registry[t] = path.Join(append([]string{Prefix}, args...)...)
 }