A single conservative amino acid substitution in the reverse transcriptase of human immunodeficiency virus type 1 confers resistance to (+)-(5S)-4,5,6,7-tetrahydro-5-methyl-6-(3-methyl-2butenyl)imidazo[4,5,1,jk][1,4] benzodiazepin-2(1H)-thione (TIBO R82150)