Michael Billington: Hamlet's sitting Tennant breaks the myth of the understudy
"Sawyer, you're going out a youngster but you've got to come back a star." So Ruby Keeler was famously told by Warner Baxter in the movie of 42nd Street. And that classic line about understudies was actually quoted by Greg Doran, director of the RSC's Hamlet, when he announced to last night's audience at the Novello that Edward Bennett was standing in for David Tennant. Mention of Edward Bennett may have prompted som…