Histograms: Ensure that the bins are aligned to an odd number of half bin widths

Histograms:  Ensure that the bins are aligned to an odd number of half bin widths

This has the benefit that the centres of the bins are aligned to integer multiples
of bin widths, and thus the labels are shorter.  For example, instead of labels
-1.5 -0.5 0.5 1.5 2.5 we get -2 -1 0 1 2 which is more aesthetically pleasing.