“Humans always tend to talk about rubbish, because they don’t really want to face the reality.” John Lennon offers this thought to a journalist in a scene from the 2000 documentary “Gimme Some Truth: The Making of John Lennon’s Imagine.” And the music on the 1971 album whose sessions are chronicled in the film certainly backs up his words — “Imagine” is the most complete and complex record in Lennon’s catalog, an expression of his greatest strengths as a singer and songwriter, and a triumph of reality, with all its contradictions, over rubbish.