SECTOR COMMENTARYEnergy stocks closed mostly lower, lagging the gains in the broader markets, while refiners and drillers bucked the trend and moved to the upside.    Downstream stocks benefited from widening crack spreads as Brent prices rose and WTI prices fell following a temporary reduction in shipping capacity on the Seaway pipeline.  The spread between the two oil grades widened to $17.55 per barrel.  Refiners received further support as a bipartisan group of more than half of U.S. Senators signed a letter urging President Barack Obama to approve the Keystone XL ...