You might not think of a short film being excellent. At least, it might not enter your mind that a 10 minute film would stack up to the impact of a full length feature. In this and other ways, aspiring short films face a tougher challenge than feature films. That said, "Birthdate," is an excellent short amongst several inviting programs of shorts at the ninth Nevada City Film Festival, Aug. 20-23. Throughout its 10 minutes, you care how a middle-aged woman and a young man handle themselves and where the connection will lead. You care how emotional and controversial the …