ABUJA, June 3 (Reuters) – Nigerian police on Sunday said the president of the upper house of parliament had been invited for questioning over allegations that he financed a criminal gang that carried out a spate of armed robberies and killed 33 people including pregnant women. Bukola Saraki’s three-year tenure as Senate president has been marred by numerous accusations of misconduct and investigations, though he has consistently stated that he is innocent and none have led to convictions. The Nigeria…