By Bill Marx “The Boys of Winter” Written by Barry Brodsky, Eric Small and Dean B. Kaner. Directed by Bridget Kathleen O’Leary. Presented by BKS Productions at Boston Playwrights Theatre, Boston, MA, through September 21. John Greiner-Ferris as the disgruntled vet in “The Boys of Winter” In his superb new essay collection “Writing in the…