Fix typos and grammar in the code

The large majority of these have been introduced by recent commits done
in the v18 development cycle.

Author: Alexander Lakhin <exclusion@gmail.com>
Discussion: https://postgr.es/m/9a7763ab-5252-429d-a943-b28941e0e28b@gmail.com

src/interfaces/libpq/fe-auth-oauth-curl.c

@@ -1205,7 +1205,7 @@ register_socket(CURL *curl, curl_socket_t socket, int what, void *ctx,
 	res = epoll_ctl(actx->mux, op, socket, &ev);
 	if (res < 0 && errno == EEXIST)
 	{
-		/* We already had this socket in the pollset. */
+		/* We already had this socket in the poll set. */
 		op = EPOLL_CTL_MOD;
 		res = epoll_ctl(actx->mux, op, socket, &ev);
 	}

src/interfaces/libpq/fe-cancel.c

@@ -50,7 +50,7 @@ struct pg_cancel
 									 * retransmits */
 
 	/* Pre-constructed cancel request packet starts here */
-	int32		cancel_pkt_len; /* in network-byte-order */
+	int32		cancel_pkt_len; /* in network byte order */
 	char		cancel_req[FLEXIBLE_ARRAY_MEMBER];	/* CancelRequestPacket */
 };
 

src/interfaces/libpq/fe-connect.c

@@ -693,7 +693,7 @@ pqDropServerData(PGconn *conn)
 	conn->oauth_want_retry = false;
 
 	/*
-	 * Cancel connections need to retain their be_pid and be_key across
+	 * Cancel connections need to retain their be_pid and be_cancel_key across
 	 * PQcancelReset invocations, otherwise they would not have access to the
 	 * secret token of the connection they are supposed to cancel.
 	 */

src/interfaces/libpq/fe-protocol3.c

@@ -1486,7 +1486,7 @@ pqGetNegotiateProtocolVersion3(PGconn *conn)
 	return 0;
 
 eof:
-	libpq_append_conn_error(conn, "received invalid protocol negotation message: message too short");
+	libpq_append_conn_error(conn, "received invalid protocol negotiation message: message too short");
 failure:
 	conn->asyncStatus = PGASYNC_READY;
 	pqSaveErrorResult(conn);