Three miscellaneous improvements for Vim

I’m wary of setting things. There is a difference between not setting things, and setting and allowing people to override them. I expect that users will tend to have certain behaviour that they want, and setting 'foldlevel' would change it from the uniform behaviour that they have set up, requiring them to set it again or suffer. I think we are best leaving the user to enable folding if they want it—the brace-based approach used at present is clumsy enough that I doubt most people would really want it anyway.