gnu: Use the 'patches' field of <origin>.

* gnu/packages/apr.scm,
  gnu/packages/autotools.scm,
  gnu/packages/avahi.scm,
  gnu/packages/cdrom.scm,
  gnu/packages/cmake.scm,
  gnu/packages/cpio.scm,
  gnu/packages/cross-base.scm,
  gnu/packages/emacs.scm,
  gnu/packages/flex.scm,
  gnu/packages/fontutils.scm,
  gnu/packages/glib.scm,
  gnu/packages/grub.scm,
  gnu/packages/guile.scm,
  gnu/packages/idutils.scm,
  gnu/packages/libevent.scm,
  gnu/packages/linux.scm,
  gnu/packages/mail.scm,
  gnu/packages/make-bootstrap.scm,
  gnu/packages/mp3.scm,
  gnu/packages/oggvorbis.scm,
  gnu/packages/pdf.scm,
  gnu/packages/plotutils.scm,
  gnu/packages/qemu.scm,
  gnu/packages/recutils.scm,
  gnu/packages/rush.scm,
  gnu/packages/scheme.scm,
  gnu/packages/system.scm,
  gnu/packages/tcsh.scm,
  gnu/packages/valgrind.scm,
  gnu/packages/vpn.scm,
  gnu/packages/w3m: Use the 'patches' field of <origin> instead of
  adding a patch as input plus using #:patches.

gnu: Revert inputs from gtk+-3 to gtk+-2.

* gnu/packages/cdrom.scm (dvdisaster): Replace input gtk+ by gtk+-2.
* gnu/packages/emacs.scm (emacs): Replace input gtk+ by gtk+-2.
* gnu/packages/geeqie.scm (geeqie): Replace input gtk+ by gtk+-2.
* gnu/packages/gkrellm.scm (gkrellm): Replace input gtk+ by gtk+-2.
* gnu/packages/mp3.scm (ripperx): Replace input gtk+ by gtk+-2.
* gnu/packages/scheme.scm: Drop duplicate inclusion of module gtk.

gnu: Add ripperX.

* gnu/packages/mp3.scm (ripperx): New variable.
* gnu/packages/patches/ripperx-libm.patch: New file.
* gnu-system.am (dist_patch_DATA): Add patch.

gnu: Add lame.

* gnu/packages/mp3.scm (lame): New variable.

gnu: Add mpg321.

* gnu/packages/mp3.scm (mpg321): New variable.

gnu: Add id3lib.

* gnu/packages/mp3.scm (id3lib): New variable.

gnu: Add libmp3splt and mp3splt.

* gnu/packages/mp3.scm (libmp3split, mp3splt): New variables.

gnu: Add libid3tag.

* gnu/packages/mp3 (libid3tag): New variable.

gnu: Add libmad.

* gnu/packages/mp3.scm: New file.
* Makefile.am (MODULES): Add it.