GLOBAL MARKETS-Oil slide hits energy shares but Alcoa cheers some

* Oil extends slide close to $45 a barrel* Energy shares hit but Alcoa cites low energy costs* Dollar hit one-month low vs yen before recoveringBy Nigel StephensonLONDON, Jan 13 (Reuters) - Oil prices slid on Tuesday to their lowest in almost six years, depressing energy shares but cheering those investors who focused on stocks seen as likely to benefit from cheaper fuel costs.The dollar hit its w