By Robert Harvey LONDON (Reuters) -The global oil market will tighten in the medium to longer term, a range of oil industry executives said in London this week, maintaining optimism despite a near-term glut driven by rising output. Production decline rates, which could accelerate as prices fall, will help to rebalance the oil market as longer-term demand is supported by rising consumption from emerging economies, the executives said. The global oil market surplus will reach 3.6 million barrels per day i ...