fix char color for VTK < 8.2, remove CHUNKSIZE

EDIT:

apparently cmake autodection of versions is not sufficient when regressions can appear in external libraries. https://answers.launchpad.net/yade/+question/695081

In CMakeLists.txt I was trying to detect possible g++ versions and boost versions to determine if more than one precision can work. I did not foresee the possibility that regressions might appear. I suspect that Su Kan compilation error is a regression in a new boost version. So although it is enabled by default (and was enabled for past year), I add an option ENABLE_REALHP to allow disabling it when necessary :)

I remove CHUNKSIZE, with ccache it is not useful anymore. And it was FTBFS: too many various chunk combinations to check for fixing, all checks would be non-ccached.

I fix compilation with VTK 8.2.

About ENABLE_REALHP see comments below, and tell me what you think.

Related problems are in #188 (closed) and #189, they are not fixed here.