guix system: Improve error messages.

* guix/ui.scm (report-error): Export.
* guix/scripts/system.scm (read-operating-system): Report syntax errors
  using standard GNU format.  Report other errors using 'display-error'.

gnu: Add convenience macros to make module imports more concise.

* gnu.scm (use-package-modules, use-service-modules,
  use-system-modules): New macros.

store: Change 'run-with-store' to return a single value.

* guix/store.scm (run-with-store): Wrap 'run-with-state' in
  'call-with-values'.  Return only the first value.

gnu: libtool: Update to 2.4.5.

* gnu/packages/autotools.scm (libtool): Update to 2.4.5.
  (libltdl): Adjust 'version' and 'source' to remain at 2.4.4.

gnu: phonon: Shuffle inputs.

* gnu/packages/kde.scm (phonon): Move automoc to native-inputs and qt to
    propagated inputs.

gnu: phonon: Update to 4.8.3.

* gnu/packages/kde.scm (phonon): Update to 4.8.3.

gnu: perf: Install libraries to lib/ instead of lib64/.

* gnu/packages/linux.scm (perf)[arguments]: Add "lib=lib" to
  #:make-flags.

gnu: perf: Build the interactive TUI.

* gnu/packages/linux.scm (perf)[inputs]: Add SLANG.

gnu: Add S-Lang.

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

gnu: perf: Build the documentation.

* gnu/packages/linux.scm (perf)[inputs]: Uncomment documentation inputs.

gnu: perf: Add dependency on Python.

* gnu/packages/linux.scm (perf)[inputs]: Add PYTHON-2.

gnu: Register patches for installation.

* gnu-system.am (dist_patch_DATA): Add patches for aegis, clucene,
    libcanberra and lua-5.1.

gnu: Add python-rdflib.

* gnu/packages/rdf.scm (python-rdflib): New variable.

gnu: Add python-html5lib.

* gnu/packages/python.scm (python-html5lib, python2-html5lib): New variables.

guix package: Avoid spurious warnings from 'find-files'.

Reported by Andreas Enge <andreas@enge.fr>.

* guix/scripts/package.scm (with-null-error-port): New macro.
  (search-path-environment-variables): Wrap 'search-path-as-list' call
  in 'with-null-error-port'.

gnu: Add python-isodate.

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

build: Make sure only the local .go files are loaded during compilation.

Reported by Andreas Enge <andreas@enge.fr>
at <http://lists.gnu.org/archive/html/guix-devel/2015-01/msg00272.html>.

* Makefile.am (.scm.go): Add "unset GUILE_LOAD_COMPILED_PATH".

gnu: 'search-patch' raises an error when a patch is not found.

* gnu/packages.scm (search-patch): Raise an error condition when
  'search-path' returns #f.
* tests/packages.scm ("patch not found yields a run-time error"): New
  test.

packages: Mark the 'patches' field as delayed.

* guix/packages.scm (<origin>)[patches]: Mark as 'delayed'.
  (print-origin, origin->derivation): Add call to 'force' when accessing
  'patches'.

records: Add support for delayed fields.

* guix/records.scm (make-syntactic-constructor): Add #:delayed
  parameter.
  [delayed-field?]: New procedure.
  [wrap-field-value]: Use it.
  (define-record-type*)[delayed-field?, wrapped-field?]: New procedures.
  [thunked-field-accessor-name]: Rename to...
  [wrapped-field-accessor-name]: ... this.
  [field-spec->srfi-9]: Change 'thunked' to 'wrapped'.
  [delayed-field-accessor-definition]: New procedure.
  Compute delayed-field accessors and emit them.  Pass #:delayed to
  'make-syntactic-constructor'.
* tests/records.scm ("define-record-type* & delayed",
  "define-record-type* & delayed & default",
  "define-record-type* & delayed & inherited"): New tests.