Allow logical replication to transfer data in binary format.

This patch adds a "binary" option to CREATE/ALTER SUBSCRIPTION.
When that's set, the publisher will send data using the data type's
typsend function if any, rather than typoutput.  This is generally
faster, if slightly less robust.

As committed, we won't try to transfer user-defined array or composite
types in binary, for fear that type OIDs won't match at the subscriber.
This might be changed later, but it seems like fit material for a
follow-on patch.

Dave Cramer, reviewed by Daniel Gustafsson, Petr Jelinek, and others;
adjusted some by me

Discussion: https://postgr.es/m/CADK3HH+R3xMn=8t3Ct+uD+qJ1KD=Hbif5NFMJ+d5DkoCzp6Vgw@mail.gmail.com

src/include/replication/pgoutput.h

@@ -20,11 +20,11 @@ typedef struct PGOutputData
 	MemoryContext context;		/* private memory context for transient
 								 * allocations */
 
-	/* client info */
+	/* client-supplied info: */
 	uint32		protocol_version;
-
 	List	   *publication_names;
 	List	   *publications;
+	bool		binary;
 } PGOutputData;
 
 #endif							/* PGOUTPUT_H */