Do not use 'created' for time anymore in Start_log_event, it's the same

as the already-stored timestamp. Now 'created' is used only to know if
this is a first binlog or not. And we may re-use the superfluous bytes
in 5.0 when we need room.


sql/log_event.cc:
  This sort of reverts a change I made in 3.23.57. In 3.23.57 I set 'created' to 0
  if this was a non-first binlog, so I made mysqlbinlog not print the "created xx"
  part if created == 0. While this was sensible, as 'created' is 0 or equal to
  the timestamp which is already stored in the event, we can always print
  "created xx" by using the timestamp, and leaving the use of 'created' only to
  know if this is a first binlog or not (which we print as "created at startup").
sql/log_event.h:
  In Start_log_event, 'created' is always the same as 'when', or O.
  We didn't need 4 bytes for this, a bit would have been enough (O or
  "same as 'when'"). Possibly in 5.0 we will re-use the useless bytes.

sql/log_event.cc

@@ -302,13 +302,11 @@ void Start_log_event::print(FILE* file, bool short_form, char* last_db)
     return;
 
   print_header(file);
-  fprintf(file, "\tStart: binlog v %d, server v %s", binlog_version,
+  fprintf(file, "\tStart: binlog v %d, server v %s created ", binlog_version,
 	  server_version);
+  print_timestamp(file);
   if (created)
-  {
-    fprintf(file, " created ");
-    print_timestamp(file, &created);
-  }
+    fprintf(file," at startup");
   fputc('\n', file);
   fflush(file);
 }

sql/log_event.h

@@ -335,6 +335,17 @@ public:
      by FLUSH LOGS or automatic rotation), 'created' should be 0.
      This "trick" is used by MySQL >=4.0.14 slaves to know if they must drop the
      stale temporary tables or not.
+     Note that when 'created'!=0, it is always equal to the event's timestamp;
+     indeed Start_log_event is written only in log.cc where the first
+     constructor below is called, in which 'created' is set to 'when'. 
+     So in fact 'created' is a useless variable. When it is 0
+     we can read the actual value from timestamp ('when') and when it is
+     non-zero we can read the same value from timestamp ('when'). Conclusion:
+     - we use timestamp to print when the binlog was created.
+     - we use 'created' only to know if this is a first binlog or not.
+     In 3.23.57 we did not pay attention to this identity, so mysqlbinlog in
+     3.23.57 does not print 'created the_date' if created was zero. This is now
+     fixed.
   */
   time_t created;
   uint16 binlog_version;