Conflicts:
	doc/manual/release-notes.xml
	doc/manual/writing-nix-expressions.xml

Apparently, turning on utf8 encoding on stderr changes its flushing
behaviour, causing sendReply to not send anything.

http://hydra.nixos.org/build/13944384

Fixes #333.

For the "stdenv accidentally referring to bootstrap-tools", it seems
easier to specify the path that we don't want to depend on, e.g.

  disallowedRequisites = [ bootstrapTools ];

I don't think it's a good idea to use allowedRequisites for stdenv, so
don't mention it here.

So all these years I was totally deluded about the meaning of "set
-e". You might think that it causes statements like "false && true" or
"! true" to fail, but it doesn't...

It turns out that using clone() to start a child process is unsafe in
a multithreaded program. It can cause the initialisation of a build
child process to hang in setgroups(), as seen several times in the
build farm:

The reason is that Glibc thinks that the other threads of the parent
exist in the child, so in setxid_mark_thread() it tries to get a futex
that has been acquired by another thread just before the clone(). With
fork(), Glibc runs pthread_atfork() handlers that take care of this
(in particular, __reclaim_stacks()). But clone() doesn't do that.

Fortunately, we can use fork()+unshare() instead of clone() to set up
private namespaces.

See also https://www.mail-archive.com/lxc-devel@lists.linuxcontainers.org/msg03434.html.

This was triggered by 47e18584, which
turned globals.state into a pointer.

Borrowed from systemd.

The Nixpkgs stdenv prints some custom escape sequences to denote
nesting and stuff like that. Most terminals (e.g. xterm, konsole)
ignore them, but some do not (e.g. xfce4-terminal). So for the benefit
of the latter, filter them out.