Bounds generator not smart enough

[Broes De Cat]

For many of the cases in the attached file, too many values are generated for x.

[Broes De Cat]

Fixes #256: Increased propsteps and longestbranch

Already had multiple examples where the approximation settings were not smart enough. Increased them already to handle the attached new example, although for some values it times out which should never happen.

→ <<cset d1dad3a61824>>