Fix another operator precedence issue found by Perl 5.20
Shut up a warning
Use posix_spawn to run the pager

In low memory environments, "nix-env -qa" failed because the fork to
run the pager hit the kernel's overcommit limits. Using posix_spawn
gets around this. (Actually, you have to use posix_spawn with the
undocumented POSIX_SPAWN_USEVFORK flag, otherwise it just uses
fork/exec...)
Define ‘environ’

http://hydra.nixos.org/build/17690555
Remove some platforms with too-old compilers
Remove Fedora 18, 19 builds

http://hydra.nixos.org/build/17703462
Use https://cache.nixos.org instead of http://cache.nixos.org
Provide some fallback defaults for the CA bundle
Add option to disable binary cache certificate checking
builtins.readFile: realise context associated with the path