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Another very minor (backwards compatibile) modification. Internally vegas processes
integration points in batches. These were called vectors initially but this name
has proven confusing, especially now that integrands can be array-valued.
To remove the potential confusion, collections of integration points are
now called batches, and: VecIntegrand is now BatchIntegrand; vecintegrand is
now batchintegrand; and nhcube_vec has become nhcube_batch. The old names
are still available, as aliases, to support legacy code.