Disable startup.jl by default?

I see you added to possibility opt-in.

It has bugged my that Julia does run it by default, but I realize it's a breaking change (hypothetically, not in practice for most) to change for Julia and for your JuliaCall.

Still I'm not sure many of your users rely on the file RUN...

I don't think Python has its own startup file, and if I'm right, even either way it's surprising to many that Julia has one. Now you need to know of it, even if you don't use one, if you send your program to others.

I think it's much faster to default to it off (also for Julia and PackageCompiler.jl).

Even if you go against the grain, I think you should, since your users could easily opt into it, those that know or care about the file.

Do you know of any good uses for it, I mean when running from the Python side? Is e.g. Revise.jl an issue, wanting it? [It's been suggested to add it to Julia.]