UPDATE 2-Russian March oil output hits new post-Soviet high

* Russia's oil output up 0.6 pct to 10.71 mln bpd in March * Total crude oil exports via Transneft up 2 pct to 4.37 mln bpd (Adds details, writes through) By Vladimir Soldatkin MOSCOW, April 2 (Reuters) - Russian oil production hit the latest in a line of post-Soviet highs in March, feeding higher exports that added to a global glut keeping crude prices low and hurting its economy. The big Gulf producers of OPEC have opted for holding on to market share, saying they will only c