Please review: [Bug 675265] preventryusn gets added to entries on a failed delete

[Noriko Hosoi]

https://bugzilla.redhat.com/show_bug.cgi?id=675265

https://bugzilla.redhat.com/attachment.cgi?id=477486&action=diff
https://bugzilla.redhat.com/attachment.cgi?id=477486&action=edit

Description: When an entry is deleted with Entry USN plugin enabled,
an operational attribute preventryusn is added to handle indexes and
entryusn tombstone.  The attribute must have been added only when
the delete was successful, but it was added regardless of the result
from the operation.  This patch checks the delete result in the
newly added entryusn delete bepost plugin (usn_bepostop_delete).
If it is not successful, the bepost plugin cleans up the attribute.