wmaker: update error message to have only one string to be translated

As a previous patch modified some instances of the error message to include
more information to the user, it is a good idea to update also the other
uses of the message, so that:
 - people helping on translation will have less messages to translate
 - this mean we provide more information to the user in these places too,
which can help him solve the problem

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>
Signed-off-by: Carlos R. Mafra <crmafra@gmail.com>

po/ja.po

@@ -1137,8 +1137,8 @@ msgstr "%s:メニューファイルのオープン／プリプロセスができ
 
 #: ../src/rootmenu.c:1105 ../src/rootmenu.c:1199
 #, c-format
-msgid "%s:could not open menu file"
-msgstr "%s:メニューファイルを開けません"
+msgid "could not open menu file \"%s\": %s"
+msgstr "メニューファイルを開けません \"%s\": %s"
 
 #: ../src/rootmenu.c:1131
 #, c-format