The cast for director Jon Turtletaub’s (National Treasure) upcoming comedy Last Vegas is firming up.  Described as “The Hangover with old guys,” the film centers on four old friends who decide to throw a Las Vegas bachelor party for the only one of them who has remained single.  Michael Douglas is set as the aging bachelor, Robert De Niro plays the wet blanket of the group, and Morgan Freeman also stars.  Now Deadline reports that Kevin Kline is joining the cast as the fourth and final member of this rag-tag team of AARP members.Though Kline’s excellent comedic skills will no doubt be put to good use in Last Vegas, this news puts a bit of a damper on the prospect of Charlie Kaufman’s Frank or Francis getting off the ground soon.  The star-studded musical was to go before cameras this year, but was recently postponed due to financing issues.