Second shot at the approach One BV, Several S.

This time, the input image is not averaged, but the graph is constructed
with dataterm being the sum of the other dataterms.

	 * src/ComputeByParts.hh: Allow non optimal mode to be computed with
	 this new approach.
	 * src/ComputeByParts.hxx: Same.
	 * src/Engine.hxx: Use this approach for one BV several S option.
	 * src/TVL0DecompositionMinimizerOneBVSeveralS.hh: The approach. New.
	 * src/TVL0DecompositionMinimizerOneBVSeveralS.hxx: The approach. New.