Fast promote mode skips checkpoint at end of recovery.

pg_ctl promote -m fast will skip the checkpoint at end of recovery so that we
can achieve very fast failover when the apply delay is low. Write new WAL record
XLOG_END_OF_RECOVERY to allow us to switch timeline correctly for downstream log
readers. If we skip synchronous end of recovery checkpoint we request a normal
spread checkpoint so that the window of re-recovery is low.

Simon Riggs and Kyotaro Horiguchi, with input from Fujii Masao.
Review by Heikki Linnakangas

src/include/access/xlog_internal.h

@@ -217,6 +217,12 @@ typedef struct xl_restore_point
 	char		rp_name[MAXFNAMELEN];
 } xl_restore_point;
 
+/* End of recovery mark, when we don't do an END_OF_RECOVERY checkpoint */
+typedef struct xl_end_of_recovery
+{
+	TimestampTz end_time;
+	TimeLineID	ThisTimeLineID;
+} xl_end_of_recovery;
 
 /*
  * XLogRecord is defined in xlog.h, but we avoid #including that to keep

src/include/catalog/pg_control.h

@@ -64,6 +64,7 @@ typedef struct CheckPoint
 #define XLOG_PARAMETER_CHANGE			0x60
 #define XLOG_RESTORE_POINT				0x70
 #define XLOG_FPW_CHANGE				0x80
+#define XLOG_END_OF_RECOVERY			0x90
 
 
 /*