This is to improve consistency with other solvers, and relates
to the expression that is converted into a finite difference when
discretising:
(phi s) - (phi s)^0 = phi^0(s - s^0) + (phi - phi^0)s
^^^^^
The above marks the spot where we now use phi^0 instead of phi.
Also:
- solveGravity() interface changed to take surface volume as a parameter,
- gravity vector is now given in initGravity() instead of
solveGravity(), for consistency with the incompressible solver.
- Changed Wells constructor arg for SimulatorIncompTwophase to WellsManager.
- Insert checking code for well constrains (mostly copied from spu_2p.cpp).
Unrelated to the above changes.
- Added pressure normalization for incompressible case (from spu_2p.cpp)
