refresh: Change default to not update source files.

* guix/scripts/refresh.scm (%options): Change `--dry-run' to `--update'.
  (show-help): Adjust accordingly.
  (guix-refresh): Likewise.

ui: Add `args-fold*' and use it.

* guix/ui.scm (args-fold*): New procedure.
* guix/scripts/build.scm, guix/scripts/download.scm,
  guix/scripts/gc.scm, guix/scripts/hash.scm, guix/scripts/import.scm,
  guix/scripts/package.scm, guix/scripts/pull.scm,
  guix/scripts/refresh.scm: Use `args-fold*' instead of `args-fold'.

Merge branch 'master' into core-updates

Conflicts:
	Makefile.am
	gnu/packages/autotools.scm
	gnu/packages/guile.scm
	gnu/packages/python.scm
	gnu/packages/shishi.scm
	guix/gnu-maintenance.scm
	guix/scripts/build.scm
	guix/scripts/gc.scm
	guix/scripts/package.scm
	guix/scripts/substitute-binary.scm
	guix/ui.scm
	nix/nix-daemon/guix-daemon.cc
	test-env.in
	tests/nar.scm
	tests/store.scm

refresh: Add `--select'.

* guix/scripts/refresh.scm (%options): Add `--select'.
  (show-help): Likewise.  Augment initial help text.
  (guix-refresh)[core-package?]: New procedure.
  Use it when selecting packages.

Add `guix refresh' and related auto-update tools.

* guix/gnu-maintenance.scm (ftp-server/directory)[quirks]: Add glib.
  (package-update-path, download-tarball, package-update,
  update-package-source): New procedures.
* guix/gnupg.scm, guix/scripts/refresh.scm: New files.
* Makefile.am (MODULES): Add them.
* guix/utils.scm (file-extension): New procedure.