gnu: gettext: Rename binding to 'gnu-gettext'.

gnu: gettext: Rename binding to 'gnu-gettext'.

* gnu/packages/gettext.scm (gettext): Rename to...
  (gnu-gettext): ... this.  This is used to work around the circular
  dependency introduced in commit c42a4b7, which users with a #:renamer
  cannot cope with.
* gnu/packages/acl.scm, gnu/packages/attr.scm, gnu/packages/cdrom.scm,
  gnu/packages/fdisk.scm, gnu/packages/gkrellm.scm, gnu/packages/glib.scm,
  gnu/packages/gnunet.scm, gnu/packages/grub.scm, gnu/packages/linux.scm,
  gnu/packages/maths.scm, gnu/packages/nano.scm, gnu/packages/parted.scm,
  gnu/packages/system.scm, gnu/packages/version-control.scm,
  gnu/packages/vpn.scm, gnu/packages/w3m.scm, gnu/packages/wget.scm:
  Adjust accordingly.