Handle heap rewrites even better in logical decoding

Logical decoding should not publish anything about tables created as
part of a heap rewrite during DDL.  Those tables don't exist externally,
so consumers of logical decoding cannot do anything sensible with that
information.  In ab28feae2b, we worked
around this for built-in logical replication, but that was hack.

This is a more proper fix: We mark such transient heaps using the new
field pg_class.relwrite, linking to the original relation OID.  By
default, we ignore them in logical decoding before they get to the
output plugin.  Optionally, a plugin can register their interest in
getting such changes, if they handle DDL specially, in which case the
new field will help them get information about the actual table.

Reviewed-by: Craig Ringer <craig@2ndquadrant.com>

src/include/replication/output_plugin.h

@@ -26,6 +26,7 @@ typedef enum OutputPluginOutputType
 typedef struct OutputPluginOptions
 {
 	OutputPluginOutputType output_type;
+	bool		receive_rewrites;
 } OutputPluginOptions;
 
 /*

src/include/replication/reorderbuffer.h

@@ -336,6 +336,11 @@ struct ReorderBuffer
 	 */
 	void	   *private_data;
 
+	/*
+	 * Saved output plugin option
+	 */
+	bool		output_rewrites;
+
 	/*
 	 * Private memory context.
 	 */