topic: suggest to clear a topic that becomes empty We add a hint suggesting "hg topic --clear" when a topic becomes empty. This usually happens when all its changesets get public, that is when the user does a 'phase -p' or when they pull from a server. To discriminate relevant cases for which we should display the hint (and typically exclude explicit 'hg topic --clear' operation), we look for the transaction "type" to only consider 'phase' or 'push' transaction. In the latter case, the transaction name is not simply 'push-response' but it also included the remote URL so we need to match on string content.