gnu: ant: Build with GCJ.

* gnu/packages/java.scm (ant)[native-inputs]: Replace "icedtea6" with
  "gcj".

gnu: gcj-4.8, gcj: Update to default GCC version.

* gnu/packages/gcc.scm (gcj-4.8): Inherit from "gcc" package and rename
  variable to...
  (gcj): ...this new variable.
  (ecj-bootstrap-4.8): Rename variable to...
  (ecj-bootstrap): ...this, updating to version 4.9.
* gnu/packages/java.scm (icedtea6)[native-inputs]: Replace "gcj-4.8"
  with "gcj".
* gnu/packages/music.scm (tuxguitar)[native-inputs]: Likewise.

gnu: abbaye: Use 'modify-phases'.

* gnu/packages/games.scm (abbaye)[arguments]: Use 'modify-phases'.

gnu: Add manaplus.

* gnu/packages/games.scm (manaplus): New variable.

build-system/python: Memoize the results of 'package-with-python2'.

Fixes <http://bugs.gnu.org/21675>.
Reported by Cyril Roelandt <tipecaml@gmail.com>.

Before this change, the command:

  guix build python2-oslo.utils -n --no-substitutes

would take 17.5s.  After, it is down to 2.9s.
Likewise, the command:

  guix graph python2-bandit | grep python2-setuptools.*Helve| wc -l

would return 412 nodes before, all functionally equivalent, and returns
a single one now.

* guix/build-system/python.scm (package-with-explicit-python): Remove
  'p' parameter.  Change to return a one-argument memoizing procedure.
  (package-with-python2): Adjust accordingly.

hydra: Update demo OS to new service interface.

* build-aux/hydra/demo-os.scm: Import (gnu services dbus); remove
  arguments to 'dbus-service'.

doc: Update "Name Service Switch" to new service framework.

* gnu/services/avahi.scm (avahi-service): Mention the extension of
  nscd.
* doc/guix.texi (Networking Services): Update accordingly.
  (Name Service Switch): Remove '%my-base-services' example and
  explanation.

gnu: geiser: Update to 0.8.

* gnu/packages/emacs.scm (geiser): Update to 0.8.

Merge branch 'core-updates'

gnu: lilypond: Hardcode path to "gs" executable.

* gnu/packages/music.scm (lilypond)[arguments]: Add build phase
  "hardcode-path-to-gs".

gnu: Add python-traitlets.

* gnu/packages/python.scm (python-traitlets, python2-traitlets): New
  variables.

gnu: Add python-ipython-genutils.

* gnu/packages/python.scm (python-ipython-genutils,
  python2-ipython-genutils): New variables.

gnu: Add python-simplegeneric.

* gnu/packages/python.scm (python-simplegeneric, python2-simplegeneric):
  New variables.

gnu: Add python-pickleshare.

* gnu/packages/python.scm (python-pickleshare, python2-pickleshare): New
  variables.

gnu: Add python-pathpy.

* gnu/packages/python.scm (python-pathpy, python2-pathpy): New
  variables.

gnu: Add python-pytest-runner.

* gnu/packages/python.scm (python-pytest-runner, python2-pytest-runner):
  New variables.

gnu: Add python-setuptools-scm.

* gnu/packages/python.scm (python-setuptools-scm,
  python2-setuptools-scm): New variables.

gnu: Add python-pexpect.

* gnu/packages/python.scm (python-pexpect, python2-pexpect): New
  variables.

gnu: bwa: Disable on non-x86_64.

* gnu/packages/bioinformatics.scm (bwa)[supported-systems]: Add field.

gnu: sdl-union: Wrap into a procedure and export it.

Suggested by Ludovic Courtès <ludo@gnu.org>.

* gnu/packages/sdl.scm (sdl-union): Make it a procedure returning
  'sdl-union' package.
  (guile-sdl): Use it.