Re: standby recovery fails (tablespace related) (tentative patch and discussion)

v26 here.  I spent some time fighting the readdir() stuff for
Windows (so that get_dirent_type returns LNK for junction points)
but couldn't make it to work and was unable to figure out why.
So I ended up doing what do_pg_backup_start is already doing:
an #ifdef to call pgwin32_is_junction instead.  I remove the
newly added path_is_symlink function, because I realized that
it would mean an extra syscall everywhere other than Windows.

So if somebody wants to fix get_dirent_type() so that it works properly
on Windows, we can change all these places together.

I also change the use of allow_invalid_pages to
allow_in_place_tablespaces.  We could add a
separate GUC for this, but it seems overengineering.

-- 
Álvaro Herrera         PostgreSQL Developer  —  https://www.EnterpriseDB.com/
"Most hackers will be perfectly comfortable conceptualizing users as entropy
 sources, so let's move on."                               (Nathaniel Smith)