* CRB index hits 7-1/2 month bottom * Brent oil down more than half pct on the year * Copper trades below $7,652/ton, a 3-month low * Cocoa, sugar down nearly 3 pct each; gold joins slide By Barani Krishnan NEW YORK, March 1 (Reuters) - Commodities tumbled on Friday, with oil entering negative territory for the year and copper hitting a three-month low, after U.S. budget cuts and a surging dollar triggered worries about raw materials demand. Cocoa and sugar were among ot