For example, this prevents a "kvm" build on machines that don't have
KVM.

Fixes #2012.

and make it more copy-pastable.

Fixes #2396.

release notes: note that the multi-user installer is available but not selected for Linux with systemd, and the bug about selinux

Use sh <(...) syntax for installation to preserve stdin and prompting

also update installation docs to account for changes in multi-user selection

shell.nix defines the install prefix as $(pwd)/inst

Includes documentation and test.

Works for uploading and not downloading.

floating-point numbers are supported now, including the fromJSON
builtin. Reported on IRC by inquisitiv3

Maybe there is a better place to document this, which is more generic?

This removes confusing documentation. It's better to remove doc than add implementation, because Nix 1.12 will surely have new GC interface anyway.

Fixes https://github.com/NixOS/nix/issues/641

Fixes #1298

While trying to understand garbage collection it was not immediately
clear that only the runtime dependency closure of output paths
would be kept (instead of the build-time dependency closure).
This commit attempts to clarify this by expanding some of the
glossary definitions and extending the Garbage Collection
section.