readdir conftest

[Herb Lewis]

Currently in samba configure there is a test to see if readdir
is broken and then to see if it can be replaced by other calls
such as getdirentries. This tests assumes that a directory that
is opened will not do directory compaction while still open -
it uses seekdir to go to the location after deleted files. This
is not true of course for NFS mounted filesystems (or in our case
for panfs).

Where in samba do we rely on this behavior?