79th st. Boat Basin -- 79th st. on the river      Intended by Robert Moses to be the "gateway to the world" when it was built, the Boat Basin used to be home to a fair number of large yachts, though now more houseboats are moored here. Many of the full-time residents are not rich -- rather they live here to beat Manhattan rents.      The Boat Basin was not always well taken care of in the past, but recently, under the leadership of the late Chief Dockmaster Ron Boudreau (1949-1997) it underwent several large changes. Areas of the docks were opened up to the public in warm weather, kayaking facilities were added, and mooring fields were expanded. Recreational boaters have become a greater presence.      True facts: a large Hong Kong junk used to be moored here, and at one time Aristotle Onassis parked his yacht, the Christina, in mid-river.      Don't miss: Ron's Doggie Bar, created by Mr. Boudreau (picture at right). next: H & H Bagels