nix-store -l: Fetch build logs from the Internet

If a build log is not available locally, then ‘nix-store -l’ will now
try to download it from the servers listed in the ‘log-servers’ option
in nix.conf. For instance, if you have:

  log-servers = http://hydra.nixos.org/log

then it will try to get logs from http://hydra.nixos.org/log/<base
name of the store path>. So you can do things like:

  $ nix-store -l $(which xterm)

and get a log even if xterm wasn't built locally.

Makefile.config.in

@@ -10,6 +10,7 @@ PACKAGE_VERSION = @PACKAGE_VERSION@
bash = @bash@
bindir = @bindir@
bsddiff_compat_include = @bsddiff_compat_include@
curl = @curl@
datadir = @datadir@
datarootdir = @datarootdir@
dblatex = @dblatex@

doc/manual/conf-file.xml

@@ -465,6 +465,20 @@ flag, e.g. <literal>--option gc-keep-outputs false</literal>.</para>
  </varlistentry>


  <varlistentry xml:id="conf-log-servers"><term><literal>log-servers</literal></term>

    <listitem>

      <para>A list of URL prefixes (such as
      <literal>http://hydra.nixos.org/log</literal>) from which
      <command>nix-store -l</command> will try to fetch build logs if
      they’re not available locally.</para>

    </listitem>

  </varlistentry>


</variablelist>

</para>