shell/caucase.sh: Emit CRL signature check errors to stderr.

So that stdout may be more reliably used for scripting.

shell/caucase.sh

@@ -1160,7 +1160,8 @@ EOF
         printf '%s\n' "$crl" > "$cas_crl"
       else
         printf \
-          'Received CAS CRL was not signed by CAS CA certificate, skipping\n'
+          'Received CAS CRL was not signed by CAS CA certificate, skipping\n' \
+	  1>&2
       fi
       if [ $update_user -eq 1 ]; then
         updateCACertificate "${ca_anon_url}/cau" "$cau_ca"
@@ -1172,7 +1173,8 @@ EOF
           printf '%s\n' "$crl" > "$cau_crl"
         else
           printf \
-            'Received CAU CRL was not signed by CAU CA certificate, skipping\n'
+            'Received CAU CRL was not signed by CAU CA certificate, skipping\n' \
+	    1>&2
         fi
       fi
     fi