Ignore lost+found when checking if a directory is empty

When an ext2, ext3, or ext4 filesystem is mounted directly on the PGDATA directory, initdb will refuse to run because
itsees the 
lost+found directory that mke2fs created and assumes the PGDATA directory is already in use for something other than
PostgreSQL.
Attached is a patch against master which will cause a directory that contains only lost+found to still be treated as
empty.

This was previously proposed in 2001; see http://archives.postgresql.org/pgsql-hackers/2001-03/msg01194.php

--
Brian Pitts
Systems Administrator | EuPathDB Bioinformatics Resource Center
706-542-1447 | bdp@uga.edu | http://eupathdb.org