The American song repertoire is often overlooked in vocal recitals, though it wasn’t always thus; as Christine Brewer observed in her splendid recital Sunday afternoon at Hertz Hall, sopranos including Eileen Farrell, Kirsten Flagstad, Eleanor Steber, and Helen Traubel used to regularly include English-language songs in their programs. Citing those artists as primary influences, Brewer made a sele