gnu: Add mc

* gnu/packages/mc.scm: New file
* gnu/packages/patches/mc-fix-ncurses-build.patch: New patch
* gnu-system.am (GNU_SYSTEM_MODULES): Add mc.scm.
(dist_patch_DATA): Add patch

gnu: libssh2: Fix use with libssh2.pc

* gnu/packages/ssh.scm (libssh2): Pass --with-libgcrypt configure flag and
  propagate inputs.

Merge branch 'core-updates'

offload: Remove erroneous 'close-pipe' call.

* guix/scripts/offload.scm (send-files): Remove 'close-pipe' call from
  'guard' handler ('pipe' here referred to Guile's 'pipe' procedure.)

offload: Wait for the processes involved in 'guix archive --missing'.

* guix/scripts/offload.scm (send-files): Keep the second return value of
  'filtered-port'.  Call 'waitpid' on it.

gnu: gp2c: Upgrade to 0.0.8pl1.

* gnu/packages/algebra.scm (gp2c): Upgrade to 0.0.8pl1, add native input perl.

offload: Allow one transfer in each direction simultaneously.

* guix/scripts/offload.scm (transfer-and-offload): Use 'upload' lock
  instead of 'bandwidth' around 'send-files' calls, and 'download' lock
  around 'retrieve-files' call.

offload: Disable SSH-level compression.

* guix/scripts/offload.scm (remote-pipe): Remove '-z' lsh command line
  argument.  This makes transfers almost an order of magnitude slower.
  OpenSSH's ssh(1) man page notes: "Compression is desirable on modem lines
  and other slow connections, but will only slow down things on fast
  networks."  See also
  <http://www.spikelab.org/blog/transfer-largedata-scp-tarssh-tarnc-compared.html>.

gnu: pari-gp: Upgrade to 2.7.0.

* gnu/packages/algebra.scm (pari-gp): Upgrade to 2.7.0.

gnu: gnu-pw-mgr: Upgrade to 1.2

* gnu/packages/gnu-pw-mgr.scm: Upgrade to 1.2

check-available-binaries: Make sure substitutes are enabled.

* build-aux/check-available-binaries.scm: Add call to
  'set-build-options'.

hydra: Hard-code target systems.

* build-aux/hydra/gnu-system.scm (hydra-jobs)[systems]: Define locally,
  independently of ARGUMENTS.  This matches the new Hydra convention,
  where using a 'system' input is deprecated.

gnu: guile-ssh: Upgrade to 0.6.0.

* gnu/packages/ssh.scm (guile-ssh): Upgrade to 0.6.0.
  [arguments]: Remove #:tests? #f; add #:parallel-build? #f.

gnu: recutils: Upgrade to 1.7.

* gnu/packages/recutils.scm (recutils): Upgrade to 1.7.
  Add 'arguments' field.

download: Don't use 'http-get*' on Guile 2.0.10+.

* guix/build/download.scm (http-fetch)[post-2.0.7?]: Use
  'string->number' and numeric comparison.  This fixes version
  comparison with "2.0.10" and subsequent 2.0 releases.

gnu: Add cursynth

* gnu/packages/cursynth.scm: New file
* gnu-system.am (GNU_SYSTEM_MODULES): Add it

gnu: remove python-fix-dbm.patch

* gnu/packages/patches/python-fix-dbm.patch: remove file. It is not needed
  anymore, and is probably a left-over of a failed merge.
* gnu-system.am: remove gnu/packages/patches/python-fix-dbm.patch

gnu: Enable tests in Python 3.

* gnu/packages/python.scm: enable tests for Python 3
* gnu/packages/python-fix-tests.patch: New file.
* gnu/packages/gnu-system.am (dist_patch_DATA): add it.

gnu: Python: use /nix/.../sh instead of /bin/sh in the subprocess module

* gnu/packages/python.scm (python-2): patch Lib/subprocess.py to use
  /nix/.../sh.

gnu: Enable the 'ctypes' module in Python.

* gnu/packages/python.scm (python-2): add libffi to the inputs and use it to
  build the ctypes module.