Avoid hot standby cancels from VAC FREEZE

VACUUM FREEZE generated false cancelations of standby queries on an
otherwise idle master. Caused by an off-by-one error on cutoff_xid
which goes back to original commit.

Backpatch to all versions 9.0+

Analysis and report by Marco Nenciarini

Bug fix by Simon Riggs

Author: simonat2ndQuadrant

src/backend/access/heap/heapam.c

@@ -7064,7 +7064,13 @@ heap_xlog_freeze_page(XLogRecPtr lsn, XLogRecord *record)
 	 * consider the frozen xids as running.
 	 */
 	if (InHotStandby)
-		ResolveRecoveryConflictWithSnapshot(cutoff_xid, xlrec->node);
+	{
+		TransactionId latestRemovedXid = cutoff_xid;
+
+		TransactionIdRetreat(latestRemovedXid);
+
+		ResolveRecoveryConflictWithSnapshot(latestRemovedXid, rnode);
+	}
 
 	/* If we have a full-page image, restore it and we're done */
 	if (record->xl_info & XLR_BKP_BLOCK(0))