broker: add year to log timestamps

Problem: Flux broker log timestamps do not contain the year. This
makes it difficult for users to determine when an error or other
log message occurred in historical job output files.

Add the year to log timestamps emitted by the broker.

src/broker/log.c

@@ -421,14 +421,16 @@ static void log_timestamp (FILE *fp,
     struct timeval tv;
     char datetime[16]; /* 'MMM DD HH:MM:SS' */
     char timezone[16]; /* TZ abbrev should be short, give 15 chars max */
+    char year[5];      /* 4 digit year */
 
     if (flags & LOG_NO_TIMESTAMP)
         return;
     if (timestamp_parse (hdr->timestamp, &tm, &tv) < 0
         || strftime (datetime, sizeof (datetime), "%b %d %T", &tm) == 0
-        || strftime (timezone, sizeof (timezone), "%Z", &tm) == 0)
+        || strftime (timezone, sizeof (timezone), "%Z", &tm) == 0
+        || strftime (year, sizeof (year), "%Y", &tm) == 0)
         fprintf (fp, "%s ", hdr->timestamp);
-    fprintf (fp, "%s.%06ld %s ", datetime, (long)tv.tv_usec, timezone);
+    fprintf (fp, "%s.%06ld %s %s ", datetime, (long)tv.tv_usec, timezone, year);
 }
 
 /* Log a message to 'fp', if non-NULL.