* guix/ui.scm (define-diagnostic): New macro, which is based on the
previous version of 'warning'.
(warning, leave): Redefine using 'define-diagnostic'.
(report-error): New macro.
(install-locale): Use 'warning' instead of 'format'.
(call-with-error-handling): Adjust 'leave'.
* gnu/packages.scm (package-files): Use 'warning' instead of 'format'.
* guix/gnu-maintenance.scm (http-fetch): Use 'warning' and 'leave'.
* guix/scripts/build.scm (derivations-from-package-expressions, guix-build):
Adjust 'leave'.
* guix/scripts/download.scm (guix-download): Adjust 'leave'.
* guix/scripts/gc.scm (size->number, %options): Adjust 'leave'.
* guix/scripts/package.scm (roll-back, guix-package): Adjust 'leave'.
* po/POTFILES.in: Add 'guix/gnu-maintenance.scm'.
* gnu/packages.scm (fold2): Remove.
* guix/utils.scm (fold2): New procedure. Generalization of the above to
one and two lists.
* tests/utils.scm ("fold2, 1 list", "fold2, 2 lists"): New tests.
* gnu/packages.scm (find-newest-available-packages):
New exported procedure.
* guix-build.in (newest-available-packages, find-best-packages-by-name):
New procedures.
(find-package): Use find-best-packages-by-name, to guarantee that
if a version number is not specified, only the newest versions will
be considered.
* guix-package.in (%options): Add --upgrade/-u option.
(newest-available-packages, find-best-packages-by-name, upgradeable?):
New procedures.
(find-package): Use find-best-packages-by-name, to guarantee that
if a version number is not specified, only the newest versions will
be considered.
(process-actions): Implement upgrade option.
* doc/guix.texi (Invoking guix-package): In the description of --install,
mention that if no version number is specified, the newest available
version will be selected.
