Rename protocol extensions to protocol options in docs

Currently we call connection parameters that have the "_pq_." prefix
both "protocol options" and "protocol extensions". This standardizes on
calling them "protocol options". The primary reason to do this is so
people don't associate them with Postgres extensions, with which they
have nothing to do. They are completely separate things, and Postgres
extensions currently cannot even define their own protocol options.

Author: JelteF

doc/src/sgml/protocol.sgml

@@ -6066,7 +6066,7 @@ psql "dbname=postgres replication=database" -c "IDENTIFY_SYSTEM;"
 
          In addition to the above, other parameters may be listed.
          Parameter names beginning with <literal>_pq_.</literal> are
-         reserved for use as protocol extensions, while others are
+         reserved for use as protocol options, while others are
          treated as run-time parameters to be set at backend start
          time.  Such settings will be applied during backend start
          (after parsing the command-line arguments if any) and will

src/backend/backup/basebackup_copy.c

@@ -9,7 +9,7 @@
  * the course of that single COPY OUT. Each CopyData message begins with a
  * type byte, allowing us to signal the start of a new archive, or the
  * manifest, by some means other than ending the COPY stream. This also allows
- * for future protocol extensions, since we can include arbitrary information
+ * for future protocol options, since we can include arbitrary information
  * in the message stream as long as we're certain that the client will know
  * what to do with it.
  *

src/interfaces/libpq/fe-protocol3.c

@@ -1439,8 +1439,8 @@ pqGetNegotiateProtocolVersion3(PGconn *conn)
 	if (num > 0)
 	{
 		appendPQExpBuffer(&conn->errorMessage,
-						  libpq_ngettext("protocol extension not supported by server: %s",
-										 "protocol extensions not supported by server: %s", num),
+						  libpq_ngettext("protocol option not supported by server: %s",
+										 "protocol options not supported by server: %s", num),
 						  buf.data);
 		appendPQExpBufferChar(&conn->errorMessage, '\n');
 	}