ui: Handle SRFI-35 '&message' conditions.

* guix/ui.scm (call-with-error-handling): Add case for
  'message-condition?'.
* po/Makevars: Fix typo in comment.

nar: 'write-file' can write to non-file ports.

* guix/nar.scm (write-contents): Use 'sendfile' only when P is a file
  port.
* tests/nar.scm ("write-file supports non-file output ports"): New test.

gnu: mpc123: Add patch that fixes a segfault.

* gnu/packages/patches/mpc123-initialize-ao.patch: New file.
* gnu/packages/mp3.scm (mpc123): Use it.
* gnu-system.am (dist_patch_DATA): Add it.

gnu: emacs: Add more inputs: giflib, libice, libsm, alsa-lib.

* gnu/packages/emacs.scm (emacs): Add 'giflib', 'libice', 'libsm', and
  'alsa-lib' inputs.  Remove "--with-gif=no" from configure arguments.

gnu: Add giflib.

* gnu/packages/giflib.scm: New file.
* gnu-system.am (GNU_SYSTEM_MODULES): Add it.

gnu: gmime: Use gnome mirror for download.

* gnu/packages/mail.scm (gmime): Use gnome mirror, fixes download problems
    with automatic https redirection.

gnu: hurd: Add MiG.

* gnu/packages/hurd.scm (mig): New variable.

Co-authored-by: Ludovic Courtès <ludo@gnu.org>
Signed-off-by: Ludovic Courtès <ludo@gnu.org>

guix hash: Don't load the whole file in memory.

* guix/scripts/hash.scm (guix-hash)[eof->null]: Remove.
  (guix-hash): Use 'port-sha256' to compute the hash instead of
  'get-bytevector-all' and co.

gnu: tor: Upgrade to 0.2.4.20.

* gnu/packages/tor.scm (tor): Upgrade to 0.2.4.20.

gnu: Add gmime.

* gnu/packages/mail.scm (gmime): New variable.

gnu: gpgme: Make 'libgpg-error' a propagated input.

* gnu/packages/gnupg.scm (gpgme): Make 'libgpg-error' a propagated input.

gnu: shishi: Add more inputs for libidn and PAM support.

* gnu/packages/shishi.scm (shishi): Add 'pkg-config' native-input.
  Add 'libidn' and 'linux-pam' inputs.

gnu: calcurse: New module

* gnu/packages/calcurse.scm: New file
* gnu-system.am (GNU_SYSTEM_MODULES): Add it

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

gnu: Add /etc/shells.

* gnu/system.scm (etc-directory): Add /etc/shells.

gnu: vm: Remove '%demo-operating-system'.

* gnu/system/vm.scm (%demo-operating-system): Remove.
  (system-qemu-image, system-qemu-image/shared-store,
  system-qemu-image/shared-store-script): Adjust accordingly.

gnu: Define '%base-services'.

* gnu/services/base.scm (%base-services): New variable.
* gnu/system.scm (<operating-system>)[services]: Change the default
  value to %BASE-SERVICES.
* doc/guix.texi (Using the Configuration System): Change
  '%standard-services' to '%base-services'.

gnu: Introduce the (gnu services ...) modules.

* gnu/system/dmd.scm: Remove file.  Move contents to...
* gnu/services.scm, gnu/services/base.scm, gnu/services/dmd.scm,
  gnu/services/networking.scm, gnu/services/xorg.scm: ... here.  New
  files.
* gnu/system.scm, gnu/system/vm.scm: Adjust accordingly.
* guix/scripts/system.scm (%user-module): Likewise.
* doc/guix.texi (Using the Configuration System): Likewise.
  (Defining Services): Likewise.

gnu: bigloo: Upgrade to 4.1a.

* gnu/packages/scheme.scm (bigloo): Upgrade to 4.1a.

gnu: qemu: Disable debug info.

* gnu/packages/qemu.scm (qemu-headless): Add '--disable-debug-info' as a
  'configure' flag.

Add 'guix system'.

* guix/scripts/system.scm: New file.
* Makefile.am (MODULES): Add it.
* po/POTFILES.in: Likewise.
* doc/guix.texi (Using the Configuration System): Link to "Invoking guix
  system".
  (Invoking guix system): New node.