list-runtime-roots: Ignore PIDs we cannot access.

This allows running as non-root.
Fixes a regression introduced in b8f59cdc20e9d83ce63523ef917e95fcee07f134.

* nix/scripts/list-runtime-roots.in (referenced-files): Handle EACCES in
addition to ENOENT.

download: Use HTTPS for the first ImageMagick mirror.

* guix/download.scm (%mirrors)[imagemagick]: Use HTTPS for <sunsite.icm.edu.pl>.

download: Try FTP servers last.

* guix/download.scm (%mirrors)[savannah, kernel.org, apache, xorg, imagemagick]:
Re-arrange so that FTP is last.

gnu: imagemagick: Update to 6.9.9-23.

* gnu/packages/imagemagick.scm (imagemagick): Update to 6.9.9-23.

list-runtime-roots: Canonicalize store items.

Looking at 'addAdditionalRoots' in libstore/gc.cc, it looks like it
should always have been this way.  In practice it probably doesn't make
much of a difference.

* nix/scripts/list-runtime-roots.in (canonicalize-store-item): New
procedure.
<top level>: Use it.

list-runtime-roots: Do not use 'lsof'.

This makes things a bit faster (0.8s instead of 1.4s on my laptop).

* nix/scripts/list-runtime-roots.in (lsof-roots): Remove.
(proc-fd-roots): Return the empty list when 'scandir' returns #f.
(referenced-files): New procedure.
Use it at the top level.

doc: Better explain GC roots.

Fixes <https://bugs.gnu.org/24194>.
Reported by J. Eppler <j.eppler@openmailbox.org>.

* doc/guix.texi (Invoking guix-daemon): Add index entries for GC roots.
Add xref to "Invoking guix gc".
(Invoking guix gc): Add the string "GC roots"; mention /var/guix/gcroots.
(Additional Build Options): Add index entries.  Better explain --root.
(Invoking guix environment): Add xref to "Invoking guix gc".

gnu: Remove unrar.

This package is abandoned upstream and contains serious bugs:

http://seclists.org/oss-sec/2017/q3/329
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-14120
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-14121
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-14122

* gnu/packages/compression.scm (unrar): Remove variable.

gnu: linux-libre: Change URL to HTTPS.

* gnu/packages/linux.scm (linux-libre): Change URL to HTTPS.

Signed-off-by: Leo Famulari <leo@famulari.name>

gnu: mupdf: Unbundle mujs.

* gnu/packages/pdf.scm (mupdf)[source]: Remove bundled mujs.
[inputs]: Add mujs.

gnu: Add mujs.

* gnu/packages/javascript.scm (mujs): New variable.

gnu: mupdf: Use https.

* gnu/packages/pdf.scm (mupdf)[source]: Use https.
[home-page]: Same.

gnu: pdf.scm: Arrange modules alphabetically.

* gnu/packages/pdf.scm: Arrange modules alphabetically.

gnu: lash: Don't build static libraries.

* gnu/packages/audio.scm (lash)[arguments]: Add configure-flag to
disable static libraries.

gnu: lash: Don't build lashd.

This fixes bug#28174.

* gnu/packages/audio.scm (lash)[arguments]: Add phase to skip building lashd.

gnu: glib-networking: Update to 2.54.1.

* gnu/packages/gnome.scm (glib-networking): Update to 2.54.1.

gnu: ffmpeg: Reduce the size of the closure.

* gnu/packages/video.scm (ffmpeg)[arguments]: Add new configure flags to
disable the html man pages and the static libraries.

gnu: mupdf: Use Texinfo for the description.

* gnu/packages/pdf.scm (mupdf)[description]: Use Texinfo to mark up the
description.

gnu: w3m: Find an editor in the environment.

* gnu/packages/w3m.scm (w3m)[arguments]: Pass an empty value for --with-editor
in #:configure-flags.
[source]: Use git-file-name.

gnu: mupdf: Actually fix CVE-2017-15587.

The original fix could be removed by an optimizing compiler.

* gnu/packages/patches/mupdf-CVE-2017-15587.patch: Revise patch.