gnu: Consolidate libjpeg, libpng, and libtiff into one module.

* gnu/packages/image.scm: New file.
* gnu-system.am (GNU_SYSTEM_MODULES): Add image.scm and remove libjpeg.scm,
  libpng.scm, and libtiff.scm.
* gnu/packages/libjpeg.scm, gnu/packages/libpng.scm, gnu/packages/libtiff.scm:
  Delete files.
* gnu/packages/emacs.scm gnu/packages/games.scm, gnu/packages/gd.scm,
  gnu/packages/geeqie.scm, gnu/packages/ghostscript.scm,
  gnu/packages/gimp.scm, gnu/packages/gnome.scm, gnu/packages/gnunet.scm,
  gnu/packages/gnustep.scm, gnu/packages/gnuzilla.scm,
  gnu/packages/graphviz.scm, gnu/packages/gtk.scm,
  gnu/packages/imagemagick.scm, gnu/packages/inkscape.scm,
  gnu/packages/netpbm.scm, gnu/packages/pdf.scm, gnu/packages/plotutils.scm,
  gnu/packages/qemu.scm, gnu/packages/qt.scm, gnu/packages/scheme.scm,
  gnu/packages/sdl.scm, gnu/packages/slim.scm, gnu/packages/tcl.scm,
  gnu/packages/texlive.scm, gnu/packages/video.scm, gnu/packages/xiph.scm,
  gnu/packages/xorg.scm: Use (gnu packages image) module.

Merge branch 'master' into core-updates

gnu: perl-tk: Patch for i686

* gnu/packages/patches/perl-tk-x11-discover.patch: New patch.
* gnu-system.am [dist_patch_DATA]: Add it.
* gnu/packages/tcl.scm (perl-tk)[origin]: Use it.

gnu: Add perl-tk

* gnu/packages/tcl.scm (perl-tk): New variable

gnu: expect: Install man pages in share/man.

* gnu/packages/tcl.scm (expect): Add --mandir configure flag.
  Use 'let' to simplify configure flags generation.

gnu: tcl: Install man pages in share/man.

* gnu/packages/tcl.scm (tcl): Add --mandir configure flag.

gnu: Add Tk.

* gnu/packages/tcl.scm (tk): New variable.

distro: tcl: Make a `tclsh' symlink.

* gnu/packages/tcl.scm (tcl): Add a `tclsh' symlink.

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: expect: Provide the right path to `stty'.

* distro/packages/tcl.scm (expect): Add #:phases argument.

distro: tcl, expect: Enable tests.

* distro/packages/tcl.scm (tcl, expect): Remove #:tests? argument; add
  #:test-target.

distro: Add Tcl, Expect, and DejaGNU.

* distro/packages/dejagnu.scm, distro/packages/tcl.scm: New files.
* Makefile.am (MODULES): Add them.