Two cowboys are at a saloon in the Old West. After a long day of shootin, tootin, and high-falootin, they've settled down for a conversation over the finest beer in the frontier.   One says to the other, ""You ever ate a banana?"" The second cowboy replies, ""No, I hain't. What's a banana?"" ""Well, it's this new, shiny, bright yella fruit, that a bunch of ex-plor-ators found in the South America. Darn tasty, too. I'll get one to ye.""   Months pass. The two cowboys meet again …