Ready to make release candidates for 1.18 and 1.20 bugfix releases

Hi! I believe I have merged all the fixes people wanted to see in 1.18 and 1.20. Anyone who's interested please double-check that your fixes are in: 1.18: https://github.com/haskell/cabal/compare/cabal-install-v1.18.0.5...1.18 1.20: https://github.com/haskell/cabal/compare/cabal-install-v1.20.0.3...1.20 If everyone are happy with these, I will try to make some releases this weekend. -- Johan