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

`fetchurl` will now throw if given an `md5`, and the hashes have generally
been upgraded to avoid it and use `sha256` as a default. This updates the
documentation examples in the manual accordingly.

manual: add XML IDs to all builtin list entries

Update docs to describe how s3:// URLS does in fact support endpoint, region, and profile for upload

nix-profile-daemon: remove cruft

This removes part of the PATH that were being added automatically in multi-user installs:

- $HOME/.nix-profile/lib/kde4/libexec - shouldn't be needed anymore, we are now using kde5
- @localstatedir@/nix/profiles/default/lib/kde4/libexec - same as above
- @localstatedir@/nix/profiles/default - shouldn't ever contain binaries

For example, this prevents a "kvm" build on machines that don't have
KVM.

Fixes #2012.

This is primarily because Derivation::{can,will}BuildLocally() depends
on attributes like preferLocalBuild and requiredSystemFeatures, but it
can't handle them properly because it doesn't have access to the
structured attributes.

E.g. __noChroot and allowedReferences now work correctly. We also now
check that the attribute type is correct. For instance, instead of

  allowedReferences = "out";

you have to write

  allowedReferences = [ "out" ];

Fixes #2453.

Update docs to describe how s3:// URLS does in fact support endpoint, region, and profile for upload

This meant that making a typo in an s3:// URI would cause a bucket to
be created. Also it didn't handle eventual consistency very well. Now
it's up to the user to create the bucket.