Remove unneeded HAVE_UNSHARE.

* src/libstore/build.cc (CHROOT_ENABLED): Remove HAVE_UNSHARE.

* If the path ends with a slash, drop it.
* If the remaining path doesn’t contain slashes, just return it.

Fixes #574.

This breaks the build on 32-bit systems.

http://hydra.nixos.org/build/24373658

Turns out that "nix-build -vvv" with chroots enabled has been broken
for some time, because some debug message got interpreted as an error.

This can be used to implement functions like ‘imap’ (or for that
matter, ‘map’) without the quadratic complexity incurred by calling
‘++’ repeatedly.

This is a generalisation of replaceChars in Nixpkgs.

This fixes the quadratic behaviour of concatStrings/concatStringsSep
in Nixpkgs.

This reduces the number of Bindings allocations by about 10%.

Pointed out by @cstrahan, thanks!

Conflicts:
	src/libexpr/eval.cc

The value pointers of lists with 1 or 2 elements are now stored in the
list value itself. In particular, this makes the "concatMap (x: if
cond then [(f x)] else [])" idiom cheaper.

These are used thousands of times during NixOS evaluation, so it's
useful to speed them up.

Such as whether Nix is built with signed binary cache support, and the
location of the configuration file.

Turns out getgrouplist() is not POSIX.

http://hydra.nixos.org/build/23881243

This ensures that 1) the derivation doesn't change when Nix changes;
2) the derivation closure doesn't contain Nix and its dependencies; 3)
we don't have to rely on ugly chroot hacks.

In particular, hydra-queue-runner can now distinguish between remote
build / substitution / already-valid. For instance, if a path already
existed on the remote side, we don't want to store a log file.

And make exportPath() less spammy by default.

This is mostly useful for hydra-queue-runner.

Previously, to build a derivation remotely, we had to copy the entire
closure of the .drv file to the remote machine, even though we only
need the top-level derivation. This is very wasteful: the closure can
contain thousands of store paths, and in some Hydra use cases, include
source paths that are very large (e.g. Git/Mercurial checkouts).

So now there is a new operation, StoreAPI::buildDerivation(), that
performs a build from an in-memory representation of a derivation
(BasicDerivation) rather than from a on-disk .drv file. The only files
that need to be in the Nix store are the sources of the derivation
(drv.inputSrcs), and the needed output paths of the dependencies (as
described by drv.inputDrvs). "nix-store --serve" exposes this
interface.

Note that this is a privileged operation, because you can construct a
derivation that builds any store path whatsoever. Fixing this will
require changing the hashing scheme (i.e., the output paths should be
computed from the other fields in BasicDerivation, allowing them to be
verified without access to other derivations). However, this would be
quite nice because it would allow .drv-free building (e.g. "nix-env
-i" wouldn't have to write any .drv files to disk).

Fixes #173.

Fixes #572.

Don't barf trying to read a link that just got deleted.

Fixes #575.

This modification moves Attr and Bindings structures into their own header
file which is dedicated to the attribute set representation. The goal of to
isolate pieces of code which are related to the attribute set
representation. Thus future modifications of the attribute set
representation will only have to modify these files, and not every other
file across the evaluator.