ui: Add 'run-guix'.

* guix/ui.scm (guix-main): Move the code to run guix command line to ...
  (run-guix): ...here.  New procedure.  Export it.

guix/ui.scm

@@ -2,7 +2,7 @@
 ;;; Copyright © 2012, 2013, 2014, 2015 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2013 Mark H Weaver <mhw@netris.org>
 ;;; Copyright © 2013 Nikita Karetnikov <nikita@karetnikov.org>
-;;; Copyright © 2014 Alex Kost <alezost@gmail.com>
+;;; Copyright © 2014, 2015 Alex Kost <alezost@gmail.com>
 ;;; Copyright © 2014 Deck Pickard <deck.r.pickard@gmail.com>
 ;;;
 ;;; This file is part of GNU Guix.
@@ -77,6 +77,7 @@
             args-fold*
             parse-command-line
             run-guix-command
+            run-guix
             program-name
             guix-warning-port
             warning
@@ -1032,13 +1033,12 @@ found."
     (parameterize ((program-name command))
       (apply command-main args))))
 
-(define guix-warning-port
-  (make-parameter (current-warning-port)))
+(define (run-guix . args)
+  "Run the 'guix' command defined by command line ARGS.
+Unlike 'guix-main', this procedure assumes that locale, i18n support,
+and signal handling has already been set up."
+  (define option? (cut string-prefix? "-" <>))
 
-(define (guix-main arg0 . args)
-  (initialize-guix)
-  (let ()
-    (define (option? str) (string-prefix? "-" str))
   (match args
     (()
      (format (current-error-port)
@@ -1057,6 +1057,13 @@ found."
     ((command args ...)
      (apply run-guix-command
             (string->symbol command)
-              args)))))
+            args))))
+
+(define guix-warning-port
+  (make-parameter (current-warning-port)))
+
+(define (guix-main arg0 . args)
+  (initialize-guix)
+  (apply run-guix args))
 
 ;;; ui.scm ends here