Speaking of velvet ropes, Janet Jackson was very nearly denied admission to the most exclusive spot on the Billboard chart. But in the final tally, she was in control — barely. Her Velvet Rope sold 202,000 copies its first week. Nearly turning her away at the door with 200,000 units sold, the Gang Related soundtrack entered at No. 2, thanks to several ”new” tracks from Tupac Shakur, who boasts the most prodigious posthumous output since L. Ron Hubbard. Not unexpectedly, last week’s entries by the Stones and Bob Dylan slipped out of the top 10 in their second frame, leaving a still-steady Fleetwood Mac to represent the old school in these picky climes.