gnu: Move numerous "inputs" which should be "native-inputs".

* gnu/packages/avahi.scm, gnu/packages/cdrom.scm, gnu/packages/cryptsetup.scm,
  gnu/packages/curl.scm, gnu/packages/emacs.scm, gnu/packages/fontutils.scm,
  gnu/packages/gdb.scm, gnu/packages/geeqie.scm, gnu/packages/ghostscript.scm,
  gnu/packages/glib.scm, gnu/packages/gnome.scm, gnu/packages/gnunet.scm,
  gnu/packages/gnupg.scm, gnu/packages/gnuzilla.scm, gnu/packages/graphviz.scm,
  gnu/packages/groff.scm, gnu/packages/gstreamer.scm, gnu/packages/gtk.scm,
  gnu/packages/gv.scm, gnu/packages/imagemagick.scm, gnu/packages/irssi.scm,
  gnu/packages/kde.scm, gnu/packages/libcanberra.scm, gnu/packages/libtiff.scm,
  gnu/packages/linux.scm, gnu/packages/lvm.scm, gnu/packages/mp3.scm,
  gnu/packages/netpbm.scm, gnu/packages/parted.scm, gnu/packages/pdf.scm,
  gnu/packages/pulseaudio.scm, gnu/packages/qemu.scm, gnu/packages/qt.scm,
  gnu/packages/ratpoison.scm, gnu/packages/rdf.scm, gnu/packages/slim.scm,
  gnu/packages/texlive.scm, gnu/packages/version-control.scm,
  gnu/packages/video.scm, gnu/packages/vpn.scm, gnu/packages/w3m.scm,
  gnu/packages/xml.scm, gnu/packages/xnee.scm, gnu/packages/xorg.scm,
  gnu/packages/zip.scm:  Move some build-time dependencies from `inputs' to
  `native-inputs'.

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

gnu: libtiff: Add zlib support.

* gnu/packages/libtiff.scm (libtiff): Add input zlib.

distro: Rename (distro) to (gnu packages).

* distro.scm: Rename to...
* gnu/packages.scm: ... this.  Update all users accordingly.
* Makefile.am (MODULES): Adjust accordingly.
* po/POTFILES.in: Likewise.

distro: Change the module name space to (gnu ...).

* distro: Rename to...
* gnu: ... this.  Update module names accordingly.
* Makefile.am: Adjust accordingly.
* po/POTFILES.in: Likewise.
* distro.scm: Search for files under /gnu/packages instead of
  /distro/packages.
* gnu/packages/base.scm (ld-wrapper-boot3): Likewise.

distro: Add libtiff.

* distro/packages/libtiff.scm: New file.
* Makefile.am (MODULES): Add it.