Nearing its centennial, the onetime Olema schoolhouse is on the market for the first time in decades. Built in 1915, money for the one-acre property was donated by Emma Shafter Howard, a principled woman who wanted a memorial for her father and a means to save youngsters from “certain lowering influences common to many pioneer towns,” namely, gin, brandy and her cousin Payne Shafter’s Sunday horse races, as historian Jack Mason tells in “Olema, Dear…