Corrected typo

The method prototype was copied and pasted from the method above, and I
forgot to change the names of the arguments (but they were correct in
the documentation).
Downscale saturation by filling blocks to interface

The coarse-scale saturation describes the height of the interface in
the column; since we assume that all the mobile CO2 is at the top, we
can start from the top and fill down to we get to the interface, when
regenerating a 3D grid with state values.
Redefine brine pressure to be at the top

Since there is only one "pressure" unknown in the underlaying
simulator the brine and CO2 pressure should be located at the same
reference point. This also means less work to do.
Introduce ordering to elevation carriers

An elevation can be "above" another elevation. We'll use this to
figure out if the cell center is above the contact interface or not.
Update internal state after upscaling

When upscaling the pressure, we need to know where the phase contact
is (to know which pressure we are being passed); after we have upscaled
the saturation, we find the interface, and *then* do the pressure.
Upscale pressure from the top-most pressure given

Inspect the top most block and set the "upscaled" pressure as the
pressure hydrostatically adjusted up to the reference point from
there. The pressure given at the top surface is always the CO2
pressure.
Report pressure hydrostatically down column

Start out by computing the pressure for each phase at the top of the
grid, and write the hydrostatic pressure from this down the column for
that of the phases that are located in the center of the block.
Expose functionality to report results in original grid
Merge pull request #28 from rolk/028_report

Downscale state to original grid for reporting