NEW YORK – Oil prices fell below $79 a barrel in choppy trading Tuesday as investors took profits from the previous day's rally and shifted their focus back to signs of dwindling world energy demand. A falling U.S. stock market, a day after a record-breaking advance, also weighed on crude prices as oil market traders continued to fixate on equities as a barometer for the overall confidence in the shaky world economy. At the pump, retail gas price kept dropping. A gallon of regular dropped 4.3 cents overnight to a new national average of $3.163, according to auto club AAA,...