By Helen Epstein July 30 featured a Russian warhorse program at Tanglewood: Glinka’s “Overture to Ruslan and Ludmila”; Tchaikovsky’s Piano Concerto No. 1 in B-flat minor, and Prokofiev’s Music from the ballet Romeo and Juliet. These are familiar (some might say over-familiar) works for orchestra, but, of course, there’s a reason they’re still being programmed.…