backend/ipp.c: Raise alert if there is issue with cert

Currently we show more detailed info about this error in debug logs, but
since there are not many desktops to pick up our dBUS notification, it
would be great to report it in CUPS log too.

Author: zdohnal

backend/ipp.c

@@ -817,12 +817,12 @@ main(int  argc,				/* I - Number of command-line args */
 					/* Trust keywords */
     static const char	* const trust_msgs[] =
     {
-      "Credentials are OK/trusted",
-      "Credentials are invalid",
-      "Credentials have changed",
-      "Credentials are expired",
-      "Credentials have been renewed",
-      "Credentials are unknown/new"
+      _("Credentials are OK/trusted"),
+      _("Credentials are invalid"),
+      _("Credentials have changed"),
+      _("Credentials are expired"),
+      _("Credentials have been renewed"),
+      _("Credentials are unknown/new")
     };
 
     fputs("DEBUG: Connection is encrypted.\n", stderr);
@@ -847,6 +847,7 @@ main(int  argc,				/* I - Number of command-line args */
       if (trusts[trust])
       {
         update_reasons(NULL, trusts[trust]);
+	_cupsLangPrintFilter(stderr, "ALERT", "%s", trust_msgs[trust]);
         return (CUPS_BACKEND_STOP);
       }