doc: Mention 'guix environment guix'.

* doc/contributing.texi (Building from Git): Mention 'guix environment
guix'.  Remove outdated description of ./bootstrap.  Clarify a few
things.

environment: Correctly handle abnormal exits.

Fixes <http://bugs.gnu.org/21958>.

* guix/scripts/environment.scm (status->exit-code): New procedure.
(exit/status, primitive-exit/status): Use it.
* tests/guix-environment-container.sh: Add test.

tests: Skip 'guix-container-environment.sh' when support is missing.

Fixes <http://bugs.gnu.org/21410>.
Reported by Alex Vong <alexvong1995@gmail.com>.

* tests/guix-environment-container.sh: Exit with 77 when
'((@@ (guix scripts environment) assert-container-features))' fails.

doc: Remove extraneous "See."

* doc/contributing.texi (Building from Git): Remove extra "See" and use
@xref instead of @pxref.

gnu: tig: Update to 2.1.1.

* gnu/packages/version-control.scm (tig): Update to 2.1.1.

gnu: cvs: Use external zlib.

* gnu/packages/version-control.scm (cvs)[arguments]: add configure flag
  --with-exernal-zlib.

gnu: nano: Update to 2.4.3.

* gnu/packages/nano.scm (nano): Update to 2.4.3.

refresh: Rewrite '--list-dependent' in terms of (guix graph).

* guix/scripts/refresh.scm (all-packages, list-dependents): New
procedures.
(guix-refresh): Use it.

graph: Add procedures to query a node's edges.

* guix/graph.scm (%node-edges, node-edges, node-back-edges)
(node-transitive-edges): New procedures.
* tests/graph.scm ("node-edges")
("node-transitive-edges + node-back-edges"): New tests.

Add (guix graph).

* guix/scripts/graph.scm (<node-type>, <graph-backend>, emit-prologue)
(emit-epilogue, emit-node, emit-edge, %graphviz-backend, export-graph):
Move to...
* guix/graph.scm: ... here.  New file.
* guix/scripts/system.scm, tests/graph.scm: Use it.
* Makefile.am (MODULES): Add it.

gnu: parted: Update to 3.2.

* gnu/packages/disk.scm (parted): Update to 3.2.
[inputs]: Add lvm2 and remove check.  Replace readline-6.2 with its
latest version.
[native-inputs]: Add perl and python for the tests.
[arguments]: Use `modify-phases' and adapt to the new tests.
[home-page]: Use https.

gnu: Add qemu-minimal.

* gnu/packages/qemu.scm (qemu): Exchange with former QEMU-HEADLESS.
(qemu-headless): Rename to...
(qemu-minimal): ... this.  New variable.  Pass --target-list.
* gnu/packages/debug.scm (qemu-2.3.0): Inherit from QEMU-MINIMAL.
* gnu/packages/grub.scm (qemu-for-tests): Likewise.
* gnu/system/vm.scm (expression->derivation-in-linux-vm, qemu-image):
Update to name change.

doc: Fix 'geiser-guile-load-path' example.

Reported by marusich on #guix.

* doc/contributing.texi (The Perfect Setup): Wrap modifying
  'geiser-guile-load-path' into 'with-eval-after-load'.

gnu: Add Synfig Studio.

* gnu/packages/animation.scm (synfigstudio): New variable.

gnu: Add Synfig.

* gnu/packages/animation.scm (synfig): New variable.
* gnu/packages/patches/synfig-build-fix.patch: New file.
* gnu-system.am (dist_patch_DATA): Add it.

gnu: Add ETL.

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

gnu: Add MLT.

* gnu/packages/video.scm (mlt): New variable.

gnu: Add libxml++.

* gnu/packages/gnome.scm (libxml++): New variable.

gnu: slepc: Update to 3.6.2.

* gnu/packages/maths.scm (slepc): Update to 3.6.2.
  [arguments]: Append "/lib" to arpack configure flag.  Use 'inputs'
  rather than '%build-inputs' in 'configure phase.

gnu: petsc: Update to 3.6.2.

* gnu/packages/maths.scm (petsc): Update to 3.6.2.