When running as root, use build users by default

This removes the need to have a nix.conf, and prevents people from
accidentally running Nix builds as root.
Set build-max-jobs to the number of available cores by default

More zero configuration.
Install an Upstart service
Set up directories and permissions for multi-user install automatically

This automatically creates /nix/var/nix/profiles/per-user and sets the
permissions/ownership on /nix/store to 1775 and root:nixbld.
Simplify multi-user installation instructions
Fix Debian tests

These actually run as root in a VM, so they get confused.

http://hydra.nixos.org/build/10775854
Don't install Upstart job on Fedora

Also, don't install a nix.conf anymore, it's not needed.

http://hydra.nixos.org/build/10775854
Add ubuntu 14.04
Fix RPM build

We don't install a nix.conf anymore.

http://hydra.nixos.org/build/10826143
Really fix the RPM builds

http://hydra.nixos.org/build/10840199
Shortcut already-hardlinked files

If an inode in the Nix store has more than 1 link, it probably means that it was linked into .links/ by us. If so, skip.

There's a possibility that something else hardlinked the file, so it would be nice to be able to override this.

Also, by looking at the number of hardlinks for each of the files in .links/, you can get deduplication numbers and space savings.
fix typo
nix-instantiate --eval: Apply auto-arguments if the result is a function

Fixes #254.
Prepare nix-mode to be uploaded to marmalade

Signed-off-by: Ricky Elrod <ricky@elrod.me>
Preload linked hashes to speed up lookups

By preloading all inodes in the /nix/store/.links directory, we can
quickly determine of a hardlinked file was already linked to the hashed
links.
This is tolerant of removing the .links directory, it will simply
recalculate all hashes in the store.
Remove redundant code
Use the inodes given by readdir directly
Shortcut store files before lstat

readdir() already returns the inode numbers, so we don't need to call
lstat to know if a file was already linked or not.
Merge branch 'master' of github.com:wmertens/nix
Remove tab