The San Francisco Opera, forced by budget constraints to trim its season, unveiled the revised schedule of performances this week, and the results are at least somewhat encouraging, says Joshua Kosman. While the number of productions may be down, the company “has refused to compromise on some of [its] more adventurous programming decisions. The season will open Sept. 6 with the company premiere of Virgil Thomson and Gertrude Stein’s 1947 collaboration The Mother of Us All, and will also include productions of Busoni’s Doktor Faust, Shostakovich’s Lady Macbeth of Mtsensk and Janacek’s The Cunning Little Vixen.”