Board of Saudi contractor Mojil quits after three sentenced

(Adds comments by company and regulator, context) DUBAI, June 20 (Reuters) - An effort to restructure debt-burdened Saudi builder Mohammad Al Mojil Group (MMG) was thrown into doubt on Monday when the firm said its board had resigned after three people involved with the company were sentenced to jail. Last week, Saudi Arabia's stock market regulator ordered MMG to pay it damages of 1.6 billion riyals ($427 million) and sentenced three people, including founder Mohammad Al-Mojil and his son Adel