Renumber CHECKPOINT_* flags.

Commit 7dbb6069 added a new CHECKPOINT_FLUSH_ALL flag. As that
commit needed to be backpatched I didn't change the numeric values of
the existing flags as that could lead to nastly problems if any
external code issued checkpoints. That's not a concern on master, so
renumber them there.

Also add a comment about CHECKPOINT_FLUSH_ALL above
CreateCheckPoint().

src/backend/access/transam/xlog.c

@@ -7892,6 +7892,7 @@ LogCheckpointEnd(bool restartpoint)
  *	CHECKPOINT_FORCE: force a checkpoint even if no XLOG activity has occurred
  *		since the last one (implied by CHECKPOINT_IS_SHUTDOWN or
  *		CHECKPOINT_END_OF_RECOVERY).
+ *	CHECKPOINT_FLUSH_ALL: also flush buffers of unlogged tables.
  *
  * Note: flags contains other bits, of interest here only for logging purposes.
  * In particular note that this routine is synchronous and does not pay

src/include/access/xlog.h

@@ -248,13 +248,13 @@ extern bool XLOG_DEBUG;
 												 * recovery */
 #define CHECKPOINT_IMMEDIATE	0x0004	/* Do it without delays */
 #define CHECKPOINT_FORCE		0x0008	/* Force even if no activity */
+#define CHECKPOINT_FLUSH_ALL	0x0010	/* Flush all pages, including those
+										 * belonging to unlogged tables */
 /* These are important to RequestCheckpoint */
-#define CHECKPOINT_WAIT			0x0010	/* Wait for completion */
+#define CHECKPOINT_WAIT			0x0020	/* Wait for completion */
 /* These indicate the cause of a checkpoint request */
-#define CHECKPOINT_CAUSE_XLOG	0x0020	/* XLOG consumption */
-#define CHECKPOINT_CAUSE_TIME	0x0040	/* Elapsed time */
-#define CHECKPOINT_FLUSH_ALL	0x0080	/* Flush all pages, including those
-										 * belonging to unlogged tables */
+#define CHECKPOINT_CAUSE_XLOG	0x0040	/* XLOG consumption */
+#define CHECKPOINT_CAUSE_TIME	0x0080	/* Elapsed time */
 
 /* Checkpoint statistics */
 typedef struct CheckpointStatsData