- rename options but leav old names as lower-priority aliases,
  also "-dirs" -> "-paths" to get closer to the meaning
- update docs to reflect the new names (old aliases are not documented),
  including a new file with release notes
- tests need an update after corresponding changes to nixpkgs
- __noChroot is left as it is (after discussion on the PR)

release: fix #652 - PDF build after dblatex updates

... while not changing behavior when used with older nixpkgs.

nix-env --upgrade improvements

It was strange to show "upgrading" when the version was getting lower.
This is left on "upgrading" when the versions are the same,
as I can't see any better wording.

Until now, if one explicitly installed a low-priority version,
nix-env --upgrade would downgrade it by default and even with --leq.
Let's never accept an upgrade with version not matching the upgradeType.
Additionally, let's never decrease the priority of an installed package;
you can use --install to force that.

Also refactor to use variable bestVersion instead of bestName,
as only version was used from it.

Fixes https://github.com/NixOS/nixpkgs/issues/9504.

Note that this means we may have a non-functional /bin/sh in the
chroot while rebuilding Bash or one of its dependencies. Ideally those
packages don't rely on /bin/sh though.

Fixes https://github.com/NixOS/nixos-homepage/issues/46.

Fixes #616.

Fixes #609.

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.