LOS ANGELES (Reuters) - R&B singer Bruno Mars grabbed the top spot on the Billboard 200 album chart on Wednesday for the first time after discounted online prices boosted sales of "Unorthodox Jukebox" some four months after its release. Mars' album, which includes the hit "Locked Out of Heaven," sold 95,000 copies last week, according to figures from Nielsen SoundScan. Industry magazine Billboard said 64,000 units of the album were digital downloads following a one-day sale of $1.99 on Amazon.com's MP3 site. ...