Detect root

[insanitybit]

There are two reasons one might run dlfile as root.

1. By mistake. Happens all the time with curl and other cli tools.
2. On purpose so that dlfile can write out to a privileged file.

I think in an ideal world (2) wouldn't happen. Instead dlfile would pipe the data to /dev/stdout and then another tool would handle the writing of the file. That said, it's probably worth supporting it.

Further, given root, we can perform more sandboxing. I don't want dlfile to be a setuid or something like that, but if we do run as root we can access namespaces, chroot, etc. This would significantly improve the sandbox.