This commit introduces a set of consistency checks for the water
phase saturation functions. These plug into the framework
introduced in commit c3939c544 (PR #5438). We implement the
following three checks
- 0 <= SWL < 1
- 0 < SWU <= 1
- SWL <= SWCR < SWU
which collectively enable a non-negative oil saturation in the two
phase oil/water system.
