UniformXTabulated2DFunction: fix interval halving code

now the values for X and Y can be added in ascending or descending
order. The descending code path is pretty slow though, and it is still
possible to screw up the object by specifying the inputs in a totally
unsorted manner. (At this place, I don't really care about these two
things, though.)
black oil fluid system: use Rs instead of XoG and interpolate the inverse B factor

this is much closer to how things are done in Eclipse. For the
external API, nothing changes provided that only the "official" fluid
system API is used...
set CMake policies CMP0026 and CMP0048 to OLD

this is required for CMake 3.0 to stop it complaining that we access
the LOCATION target property and set the *_VERSION_* variables ourselves.
cmake: policies must be protected by if()

... unless they shall break older cmake versions which don't know
about them. this seems to be a bit superfluous to me, but whatever...