Escape text for display in password prompt.

From the Debian patch stack.

--- a/libgksu/libgksu.c
+++ b/libgksu/libgksu.c
@@ -994,12 +994,12 @@
 				     "The application '%s' lets you "
 				     "modify essential parts of your "
 				     "system."),
-				   command);
+				   g_markup_escape_text(command, -1));
 	  else
 	    msg = g_strdup_printf (_("<b><big>Enter your password to run "
 				     "the application '%s' as user %s"
 				     "</big></b>"),
-				   command, context->user);
+				   g_markup_escape_text(command, -1), context->user);
 	}
       else
 	{