linux-initrd: Gracefully deal with partitions with no label.

* guix/build/linux-initrd.scm (partition-label-predicate): Check whether
  'ext2-superblock-volume-name' returns #f, and return #f if it does.

gnu: Move libarchive to (gnu packages backup).

* gnu/packages/compression.scm (libarchive): Move to...
* gnu/packages/backup.scm (libarchive): ... here.
  Import (guix licenses) with #:renamer to avoid conflicting 'zlib'
  bindings.

vm: disk-image: Specify the root file system using a label.

* gnu/system/vm.scm (system-disk-image)[root-label]: New variable.
  Use it for the root file system, and pass it as #:file-system-label to
  'qemu-image'.

linux-initrd: Allow use of volume labels in 'file-system' declarations.

* guix/build/linux-initrd.scm (%ext2-endianness, %ext2-sblock-magic,
  %ext2-sblock-creator-os, %ext2-sblock-uuid, %ext2-sblock-volume-name):
  New macros.
  (read-ext2-superblock, ext2-superblock-uuid,
  ext2-superblock-volume-name, disk-partitions,
  partition-label-predicate, find-partition-by-label,
  canonicalize-device-spec): New procedures.
  (mount-file-system): Use 'canonicalize-device-spec' on SOURCE.
  (boot-system): Likewise for ROOT.
* doc/guix.texi (Using the Configuration System): Adjust 'file-system'
  declaration accordingly.

gnu: Add rdiff-backup.

* gnu/packages/backup.scm (rdiff-backup): New variable.

gnu: Add btar.

* gnu/packages/backup.scm (btar): New variable.

gnu: Add rdup.

* gnu/packages/backup.scm (rdup): New variable.

gnu: Add libarchive.

* gnu/packages/compression.scm (libarchive): New variable.

gnu: Add hdup.

* gnu/packages/backup.scm (hdup): New variable.

hydra: Don't cross-build from MIPS to MIPS.

* build-aux/hydra/gnu-system.scm (hydra-jobs)[same?, either]: New
  procedure.  Use it in 'remove' call.

system: Add 'fusermount' to the default setuid programs.

* gnu/system.scm (%setuid-programs): Add 'fusermount'.

vm: Allow a volume name to be specified for the root partition.

* guix/build/vm.scm (format-partition): Add #:label parameter, and honor
  it.
  (initialize-hard-disk): Add #:file-system-label parameter, and pass it
  to 'format-partition'.
* gnu/system/vm.scm (qemu-image): Add #:file-system-label parameter and
  pass it to 'initialize-hard-disk'.

gnu: libgnome: Correct source file name.

* gnu/packages/gnome.scm (libgnome): Correct source file name.

hydra: Build for mips64el-linux.

* build-aux/hydra/gnu-system.scm (hydra-jobs)[systems]: Add
  mips64el-linux.

gnu: fuse: Allow use of 'fusermount' taken from $PATH.

* gnu/packages/linux.scm (fuse) <set-file-names>: Set FUSERMOUNT_DIR in
  lib/Makefile.

gnu: Add sshfs-fuse.

* gnu/packages/linux.scm (sshfs-fuse): New variable.

gnu: Make gtk-glext depend on pangox-compat and remove workaround patch

* gnu/packages/gnome.scm (gtk-glext): Add new dependency and remove patch
* gnu/packages/patches/gtkglext-remove-pangox-dependency.patch: Delete file
* gnu-system.am: Delete gnu/packages/patches/gtkglext-remove-pangox-dependency.patch

gnu: Add cssc.

* gnu/packages/version-control.scm (cssc): New variable.
* gnu/packages/patches/cssc-gets-undeclared.patch: New file
* gnu/packages/patches/cssc-missing-include.patch: New file
* gnu-system.am: Add gnu/packages/patches/cssc-gets-undeclared.patch
  and gnu/packages/patches/cssc-missing-include.patch

gnu: hdf5: Fix source download location.

* gnu/packages/maths.scm (hdf5): Use "release" directory and not the "current"
    directory for the source, which does not break on new upstream releases.

syscalls: Be more permissive in 'umount' test.

* tests/syscalls.scm ("umount, ENOENT"): Rename to...
  ("umount, ENOENT/EPERM"): ... this.  Accept EPERM as a valid return
  value.