ui: Handle SRFI-35 '&message' conditions.

* guix/ui.scm (call-with-error-handling): Add case for
  'message-condition?'.
* po/Makevars: Fix typo in comment.

guix/ui.scm

@@ -31,6 +31,7 @@ (define-module (guix ui)
   #:use-module (srfi srfi-19)
   #:use-module (srfi srfi-26)
   #:use-module (srfi srfi-34)
+  #:use-module (srfi srfi-35)
   #:use-module (srfi srfi-37)
   #:autoload   (ice-9 ftw)  (scandir)
   #:use-module (ice-9 match)
@@ -186,7 +187,10 @@ (define (call-with-error-handling thunk)
             ((nix-protocol-error? c)
              ;; FIXME: Server-provided error messages aren't i18n'd.
              (leave (_ "build failed: ~a~%")
-                    (nix-protocol-error-message c))))
+                    (nix-protocol-error-message c)))
+            ((message-condition? c)
+             ;; Normally '&message' error conditions have an i18n'd message.
+             (leave (_ "~a~%") (gettext (condition-message c)))))
     ;; Catch EPIPE and the likes.
     (catch 'system-error
       thunk

po/Makevars

@@ -6,7 +6,7 @@ subdir = po
 top_builddir = ..
 
 # These options get passed to xgettext.  We want to catch standard
-# gettext uses, package synopses and descriptions, and SRFI-34 error
+# gettext uses, package synopses and descriptions, and SRFI-35 error
 # condition messages.
 XGETTEXT_OPTIONS =				\
   --language=Scheme --from-code=UTF-8		\