ATHENS (Reuters) - Greek President Prokopis Pavlopoulos has cancelled a trip to Berlin planned for Tuesday, which will come two days after a referendum on an international bailout, a person with knowledge of the issue said on Thursday. As head of state, Pavlopoulos would be responsible for overseeing a change of government in the event that Prime Minister Alexis Tsipras were to resign following the referendum, which is widely seen as a vote on the future of Greece in Europe. (Reporting by Lefteris Papadimas)