* Messi, father allegedly withheld over 4 million euros * Accused of filing fraudulent returns in 2006-09 * Pair deny wrongdoing in statement on Facebook (Adds details of charges) By Emma Pinedo MADRID, June 12 (Reuters) - Barcelona's Argentina forward Lionel Messi and his father denied wrongdoing on Wednesday after the Spanish tax authorities accused them of defrauding the state of more than four million euros ($5.3 million). ... More...