Bugfix: ensure that the tree-level masses, which enter the calculation
of the one-loop masses, have been calculated using the tree-level EWSB
parameters.

The problem was that solve_ewsb_one_loop() modifies Mu and BMu and
calls calculate_DRbar_parameters().  Therefore, after
solve_ewsb_one_loop() has finished, the tree-level spectrum has been
calculated with the one-loop EWSB parameters.