Plenty of scrutiny will come with being a struggling top prospect, but having vocal detractors in your own organization is certainly unusual. That’s what it appears 23-year-old Red Sox shortstop Marcelo Mayer is dealing with as he landed on the 10-day IL with a stress reaction in his forearm Friday. “Some question his mental toughness and his tendency to withdraw during slumps,” Sean McAdams of Mass Live wrote Friday ahead of Boston’s 6-1 home win over the Yankees. “Others wonder if he couldn’t