preferLocalBuild does not in fact prevent substitution.

Since we're not using multi-part uploads at the moment, we can drop
this patch.

Fix typo in comments

config: use all of XDG_CONFIG_DIRS

Previously, config would only be read from XDG_CONFIG_HOME. This change
allows reading config from additional directories, which enables e.g.
per-project binary caches or chroot stores with the help of direnv.

The use of TransferManager has several issues, including that it
doesn't allow setting a Content-Encoding without a patch, and it
doesn't handle exceptions in worker threads (causing termination on
memory allocation failure).

Fixes #2493.

Since the callback is global we can't refer to 'path' in it. This
could cause a segfault or printing of arbitrary data.

copyStorePath: Fix hash errors when copying from older store

This commit partially reverts 48662d15. When
copying from an older store (in my case a store running Nix 1.11.7), nix would
throw errors about there being no hash. This is fixed by recalculating the hash.

nix doctor: return nonzero exitcode if a check fails

This makes it easier to use this when testing the installer or when
running the checks with other automated tooling.

stdenv relies on this. So ignore self-references (but only in legacy non-structured attributes mode).

remote-store.hh: ConnectionHandle is struct, minor fix warning

src/nix/local.mk: fix typos in names of symlinks

These are all symlinks to 'nix' now, reducing the installed size by
about ~1.7 MiB.

Promote verbose-build and log-lines

This allows commands like

nix build --log-lines 30 nixpkgs.hello

in order to obtain more information in case of a failure.

Add --graphml option to the nix-store --query command

In structured-attributes derivations, you can now specify per-output
checks such as:

  outputChecks."out" = {
    # The closure of 'out' must not be larger than 256 MiB.
    maxClosureSize = 256 * 1024 * 1024;

    # It must not refer to C compiler or to the 'dev' output.
    disallowedRequisites = [ stdenv.cc "dev" ];
  };

  outputChecks."dev" = {
    # The 'dev' output must not be larger than 128 KiB.
    maxSize = 128 * 1024;
  };

Also fixed a bug in allowedRequisites that caused it to ignore
self-references.

The `--graphml` option can be used instead.

This prints the references graph of the store paths in the graphML
format [1]. The graphML format is supported by several graph tools
such as the Python Networkx library or the Apache Thinkerpop project.

[1] http://graphml.graphdrawing.org

install script: remove unportable command check, fixup errant escape

  $ nix-store -qR /nix/store/fnord
  nix-store: src/libstore/store-api.cc:80: std::__cxx11::string nix::storePathToHash(const Path&): Assertion `base.size() >= storePathHashLen' failed.
  Aborted

Fixes #2075.

Since its superclass RemoteStore::Connection contains 'to' and 'from'
fields that refer to the file descriptor maintained in the subclass,
it was possible for the flush() call in Connection::~Connection() to
write to a closed file descriptor (or worse, a file descriptor now
referencing another file). So make sure that the file descriptor
survives 'to' and 'from'.

`which` isn't necessarily portable, but `command -v` is an equivalent form.

Additionally, the `\'` is not necessary, as it is already quoted by `"`.

bump base nixpkgs used by default 18.03 -> 18.09

Fix overflow when verifying signatures of content addressable paths

Docs: update fixed output hashes