gnu: mailutils: Fix uninitialized memory bug.

This was causing segfaults in the MH test suite when building with
glibc 2.26 on x86_64.

* gnu/packages/patches/mailutils-uninitialized-memory.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/mail.scm (mailutils)[source](patches, snippet): New
fields.
[native-inputs]: New field.

gnu: gcc@4.9: Fix libsanitizer compilation with glibc 2.26.

* gnu/packages/patches/gcc-4.9-libsanitizer-fix.patch: New file.
* gnu/packages/gcc.scm (gcc-4.9)[source](patches): Add it.
* gnu/local.mk (dist_patch_DATA): Add it.

gnu: gvpe: Fix compilation against glibc 2.26.

* gnu/packages/vpn.scm (gvpe)[source](modules, snippet): New fields.

gnu: shepherd: Add dependency on guile-readline.

* gnu/packages/admin.scm (shepherd)[inputs]: Add GUILE-READLINE.

Merge branch 'master' into core-updates

gnu: geda-gaf: Disable two broken tests.

* gnu/packages/engineering.scm (geda-gaf)[arguments]: Disable two failing
tests.

gnu: Add emacs-nov-el.

* gnu/packages/emacs.scm (emacs-nov-el): New variable.

gnu: Add emacs-esxml.

* gnu/packages/emacs.scm (emacs-esxml): New variable.

gnu: python-hacking: Update to 1.0.0.

* gnu/packages/openstack.scm (python-hacking): Update to 1.0.0.
[propagated-inputs]: Change PYTHON-FLAKE8 to PYTHON-FLAKE8-2.5.
* gnu/packages/python.scm (python-flake8-2.5, python2-flake8-2.5): New public
variables.

gnu: python-defusedxml: Update to 0.5.0.

* gnu/packages/xml.scm (python-defusedxml): Update to 0.5.0.

gnu: python-waitress: Update to 1.1.0.

* gnu/packages/patches/python-waitress-fix-tests.patch: New file.
* gnu/local.mk (dist_patch_DATA): Register it.
* gnu/packages/python.scm (python-waitress): Update to 1.1.0.
[source](patches): New field.

bash completion: Complete files names after 'guix package -m'.

* etc/completion/bash/guix (_guix_is_dash_m): New function.
(_guix_complete): Add this.

gnu: libffcall: Update to 2.1.

* gnu/packages/libffcall.scm (libffcall): Update to 2.1.

gnu: btrfs-progs: Fix bash completions.

This is a follow-up to commit 9a1c4a981bdd7eeca76aaf73a57d6841918821c2.  Bash
completions must have the same name as the executable.

* gnu/packages/linux.scm (btrfs-progs)[arguments]: Rename "btrfs-completion"
script to "btrfs".

gnu: zathura: Don't propagate girara in dependent packages.

* gnu/packages/pdf.scm (zathura-cb, zathura-ps, zathura-djvu,
zathura-pdf-mupdf, zathura-pdf-poppler)[propagated-inputs]: Remove GIRARA.

gnu: zathura, girara: Use the test-only xorg variant for tests.

* gnu/packages/gtk.scm (girara)[native-inputs]: Replace XORG-SERVER with
XORG-SERVER-1.19.3.
[arguments]: Add #:disallowed-references.
* gnu/packages/pdf.scm (zathura)[native-inputs, arguments]: Likewise.

gnu: zathura: Increase test timeouts.

* gnu/packages/pdf.scm (zathura): Export CK_DEFAULT_TIMEOUT before running
tests.

gnu: girara: Increase test timeouts.

Fixes build failures on Hydra.  Reported by Mark H Weaver in
<https://lists.gnu.org/archive/html/guix-devel/2017-12/msg00391.html>.

* gnu/packages/gtk.scm (girara)[arguments]: Set CK_DEFAULT_TIMEOUT before
running tests.

gnu: ruby-2.4.3: Update rubygems to 2.7.6.

This fixes the security issues described at
https://www.ruby-lang.org/en/news/2018/02/17/multiple-vulnerabilities-in-
rubygems/

* gnu/packages/patches/ruby-rubygems-276-for-ruby24.patch: New file.
* gnu/packages/ruby.scm (ruby-2.4.3)[source]: Use it.
* gnu/local.mk (dist_patch_DATA): Add it.

gnu: ghc-mtl: Remove ghc-transformers from inputs.

* gnu/packages/haskell.scm (ghc-mtl)[arguments]: Explain why we need to allow
a newer version of the transformers package.
[inputs]: Remove ghc-transformers.