Rename pg_replication_slot's new active_in to active_pid.

In d811c037ce active_in was added but discussion since showed that
active_pid is preferred as a name.

Discussion: CAMsr+YFKgZca5_7_ouaMWxA5PneJC9LNViPzpDHusaPhU9pA7g@mail.gmail.com

contrib/test_decoding/expected/ddl.out

@@ -603,7 +603,7 @@ SELECT pg_drop_replication_slot('regression_slot');
 
 /* check that the slot is gone */
 SELECT * FROM pg_replication_slots;
- slot_name | plugin | slot_type | datoid | database | active | active_in | xmin | catalog_xmin | restart_lsn 
------------+--------+-----------+--------+----------+--------+-----------+------+--------------+-------------
+ slot_name | plugin | slot_type | datoid | database | active | active_pid | xmin | catalog_xmin | restart_lsn 
+-----------+--------+-----------+--------+----------+--------+------------+------+--------------+-------------
 (0 rows)
 

doc/src/sgml/catalogs.sgml

@@ -5401,7 +5401,7 @@
      </row>
 
      <row>
-      <entry><structfield>active_in</structfield></entry>
+      <entry><structfield>active_pid</structfield></entry>
       <entry><type>integer</type></entry>
       <entry></entry>
       <entry>The process ID of the session using this slot if the slot

src/backend/catalog/system_views.sql

@@ -665,7 +665,7 @@ CREATE VIEW pg_replication_slots AS
             L.datoid,
             D.datname AS database,
             L.active,
-            L.active_in,
+            L.active_pid,
             L.xmin,
             L.catalog_xmin,
             L.restart_lsn

src/include/catalog/pg_proc.h

@@ -5106,7 +5106,7 @@ DATA(insert OID = 3779 (  pg_create_physical_replication_slot PGNSP PGUID 12 1 0
 DESCR("create a physical replication slot");
 DATA(insert OID = 3780 (  pg_drop_replication_slot PGNSP PGUID 12 1 0 0 0 f f f f f f v 1 0 2278 "19" _null_ _null_ _null_ _null_ pg_drop_replication_slot _null_ _null_ _null_ ));
 DESCR("drop a replication slot");
-DATA(insert OID = 3781 (  pg_get_replication_slots	PGNSP PGUID 12 1 10 0 0 f f f f f t s 0 0 2249 "" "{19,19,25,26,16,23,28,28,3220}" "{o,o,o,o,o,o,o,o,o}" "{slot_name,plugin,slot_type,datoid,active,active_in,xmin,catalog_xmin,restart_lsn}" _null_ pg_get_replication_slots _null_ _null_ _null_ ));
+DATA(insert OID = 3781 (  pg_get_replication_slots	PGNSP PGUID 12 1 10 0 0 f f f f f t s 0 0 2249 "" "{19,19,25,26,16,23,28,28,3220}" "{o,o,o,o,o,o,o,o,o}" "{slot_name,plugin,slot_type,datoid,active,active_pid,xmin,catalog_xmin,restart_lsn}" _null_ pg_get_replication_slots _null_ _null_ _null_ ));
 DESCR("information about replication slots currently in use");
 DATA(insert OID = 3786 (  pg_create_logical_replication_slot PGNSP PGUID 12 1 0 0 0 f f f f f f v 2 0 2249 "19 19" "{19,19,25,3220}" "{i,i,o,o}" "{slot_name,plugin,slot_name,xlog_position}" _null_ pg_create_logical_replication_slot _null_ _null_ _null_ ));
 DESCR("set up a logical replication slot");

src/test/regress/expected/rules.out

@@ -1396,11 +1396,11 @@ pg_replication_slots| SELECT l.slot_name,
     l.datoid,
     d.datname AS database,
     l.active,
-    l.active_in,
+    l.active_pid,
     l.xmin,
     l.catalog_xmin,
     l.restart_lsn
-   FROM (pg_get_replication_slots() l(slot_name, plugin, slot_type, datoid, active, active_in, xmin, catalog_xmin, restart_lsn)
+   FROM (pg_get_replication_slots() l(slot_name, plugin, slot_type, datoid, active, active_pid, xmin, catalog_xmin, restart_lsn)
      LEFT JOIN pg_database d ON ((l.datoid = d.oid)));
 pg_roles| SELECT pg_authid.rolname,
     pg_authid.rolsuper,