python simulate() change in behaviour in sme 1.0.9

[lkeegan]

Previously to version 1.0.9 of sme, model.simulate() would always start a new simulation of the model from the initial model concentrations.

Because of the improvements to simulation in #470, in version 1.0.9 calling simulate() for a second time on the same model does something different:

• the simulation continues from where it was, not from the original model state
• but the previous simulation data is not added to the results on the python side, only the new results are visible

We should revert to the previous behaviour for now, i.e. explicitly clear any SimulationData before each simulation, to avoid breaking any existing python code that expects multiple simulate calls to the same model to be independent of each other.