Orthogonalize `maxspace`/`union` for `ConstantSpace`#327

jishnub wants to merge 1 commit intoJuliaApproximation:masterJuliaApproximation/ApproxFunBase.jl:masterfrom

jishnub:domainunionanyjishnub/ApproxFunBase.jl:domainunionanyCopy head branch name to clipboard