Comment fixes related to logical decoding.

Andres Freund, per complaints by Peter Eisentraut.

contrib/test_decoding/test_decoding.c

@@ -33,6 +33,7 @@
 
 PG_MODULE_MAGIC;
 
+/* These must be available to pg_dlsym() */
 extern void		_PG_init(void);
 extern void		_PG_output_plugin_init(OutputPluginCallbacks *cb);
 
@@ -43,7 +44,6 @@ typedef struct
 	bool		include_timestamp;
 } TestDecodingData;
 
-/* These must be available to pg_dlsym() */
 static void pg_decode_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
 							  bool is_init);
 static void pg_decode_shutdown(LogicalDecodingContext *ctx);

src/backend/replication/logical/logical.c

@@ -12,14 +12,17 @@
  *    together provide logical decoding, primarily by providing so
  *    called LogicalDecodingContexts. The goal is to encapsulate most of the
  *    internal complexity for consumers of logical decoding, so they can
- *    create and consume a changestream with a low amount of code.
+ *    create and consume a changestream with a low amount of code. Builtin
+ *    consumers are the walsender and SQL SRF interface, but it's possible to
+ *    add further ones without changing core code, e.g. to consume changes in
+ *    a bgworker.
  *
  *    The idea is that a consumer provides three callbacks, one to read WAL,
  *    one to prepare a data write, and a final one for actually writing since
  *    their implementation depends on the type of consumer.  Check
- *    logicalfunc.c for an example implementations of a fairly simple consumer
+ *    logicalfuncs.c for an example implementation of a fairly simple consumer
  *    and a implementation of a WAL reading callback that's suitable for
- *    simpler consumers.
+ *    simple consumers.
  *-------------------------------------------------------------------------
  */