clarified order: update syslog before handling exit;

--- a/src/Pure/PIDE/session.scala	Sat Mar 28 13:30:38 2020 +0100
+++ b/src/Pure/PIDE/session.scala	Sat Mar 28 13:40:55 2020 +0100
@@ -566,15 +566,15 @@
         //{{{
         arg match {
           case output: Prover.Output =>
-            if (output.is_stdout || output.is_stderr)
-              raw_output_messages.post(output)
-            else handle_output(output)
-
             if (output.is_syslog) {
               syslog += output.message
               syslog_messages.post(output)
             }
 
+            if (output.is_stdout || output.is_stderr)
+              raw_output_messages.post(output)
+            else handle_output(output)
+
             all_messages.post(output)
 
           case input: Prover.Input =>