SAN FRANCISCO — A record 61 percent of Californians now approve of allowing same-sex couples to marry, according to a poll released Thursday. The Field Poll found 78 percent support among people 39 and younger and a solid majority of middle-aged residents now back gay marriage — 56 percent. Even among senior citizens there is 48 percent support, compared with 42 percent against. The overall results represent a reversal in views about the issue in the 36 years the Field Poll has been taking surveys on gay marriage. In 1977, when the first survey was conducted, only 28 percent approved …