Unrecognized fds should be set to cloexec

[ebroder]

This can specifically be an issue with code preloading, which can, e.g., establish database connections and such.

[ebroder]

(FTR, I've recently run into a situation where I actually want to open fds before spawning children, so if we build this functionality, we should be sure to add an option to turn it off)