Option for maximum CVODE order, safer default value

[rruusu]

Current status

The maximum order for the CVODE solver is hardcoded to the value 5.

This poses several difficulties for some tightly coupled models with fast and weakly attenuated vibration modes, whose solutions exhibit unphysical oscillations and fall to very small time steps. It is made worse by numerical errors from algebraic loops between components, which introduces inaccuracies to calculated Jacobian values. (See #1327)

Proposed feature

It would be useful to have a command line option (--CVODEMaximumOrder) to be able to set it to a different value.

The default value should also be lowered to a safer level, such as 2. This may, however, slow down some simulations of less tightly coupled models.