Hartree potential has small error

[timcallow]

The Hartree potential integral is performed in two parts:

In the code this is done as:

Since we have a discrete grid we need to choose where the splitting point of the Hartree integral is (ie whether to use <= or < in the above). At the moment, it seems the split is not right when considering the integral discretization. So the inequalities need to be swapped (which makes a small difference to the numerics).