Prevent the already-archived WAL file from being archived again.

 Prevent the already-archived WAL file from being archived again.
 
 Previously the archive recovery always created .ready file for
 the last WAL file of the old timeline at the end of recovery even when
 it's restored from the archive and has .done file. That is, there was
 the case where the WAL file had both .ready and .done files.
 This caused the already-archived WAL file to be archived again.
 
 This commit prevents the archive recovery from creating .ready file
 for the last WAL file if it has .done file, in order to prevent it from
 being archived again.
 
 This bug was added when cascading replication feature was introduced,
 i.e., the commit 5286105800c7d5902f98f32e11b209c471c0c69c.
 So, back-patch to 9.2, where cascading replication was added.
 
 Reviewed by Michael Paquier