LONDON (Reuters) -OPEC oil output has fallen in April, a Reuters survey found on Tuesday, reflecting lower exports from Iran, Iraq and Nigeria against a backdrop of ongoing voluntary supply cuts by some members agreed with the wider OPEC+ alliance. The Organization of the Petroleum Exporting Countries pumped 26.49 million barrels per day (bpd) this month, down 100,000 bpd from March's revised total, the survey, based on shipping data and information from industry sources, found. Several members of OPEC+, which includes OPEC, Russia and other allies, made new cuts in January to counter e...