Computer Science and Engineering, University of California San Diego, 9500 Gilman Drive, San Diego, CA 92123 and Microsoft Research, 1065 La Avenida, Mountain View, CA 94043, USA.|Computer Science and Engineering, University of California San Diego, 9500 Gilman Drive, San Diego, CA 92123 and Microsoft Research, 1065 La Avenida, Mountain View, CA 94043, USA.|Computer Science and Engineering, University of California San Diego, 9500 Gilman Drive, San Diego, CA 92123 and Microsoft Research, 1065 La Avenida, Mountain View, CA 94043, USA.|Computer Science and Engineering, University of California San Diego, 9500 Gilman Drive, San Diego, CA 92123 and Microsoft Research, 1065 La Avenida, Mountain View, CA 94043, USA.