DETROIT — You can’t really call it a trend, but giving contract extensions to players who’ve yet to make their Major League debuts is not unprecedented, either. Tigers 22-year-old prospect Colt Keith on Sunday became the seventh active player and the second in successive months to sign a long-term contract extension without a single day of big-league service time. Keith is guaranteed $28.6 million over the next six years, plus a $2 million signing bonus. The Tigers hold options on him for three years beyond that, essentially giving them team control for nine years. If all options on escalators…