To hear Parker Posey tell it, the way she ended up as part of Christopher Guest’s go-to gang of actors for 20-plus years is a pretty typical tale of Hollywood who-knows-who connections. Posey had a tiny role in the 1993 Saturday Night Live spinoff The Coneheads, but did enough to impress producer Lorne Michaels — so much that the SNL chief recommended the young performer to Guest and his producer Karen Michaels when they were looking for an actress who could play 18 years old and improvise. P...