Ticket #630 - The backend name provided to bak2db is not validated

Bug description: backend instance name was not validated correctly.
When a given backend instance name was not valid, the instance name
was ignored and the utility restored all instances, which was a default
behaviour of the restore -- bak2db.

Fix description: This patch adds the code to check the backend instance
name.  If there is no backend instance, the restore request is ignored.
In addition, it enhanced the back up path validation, as well.

There was another bug found in the restore/bak2db.  The backend instance
name is supposed to be case insensitive, but the case was not ignored.
The bug was fixed, too.

Reviewed by Rich (Thank you!!)

https://fedorahosted.org/389/ticket/630
Ticket #415 - winsync doesn't sync DN valued attributes if DS DN value doesn't exist

Bug description:
2 case were fixed.
1) A group on AD has a member which is not a target of windows
   sync and exists only on AD.  The member value in the group is
   synchronized to DS.  If an operation is executed on AD so that
   the member is replaced with other members which are the target
   of the windows sync, the new member values are not synchronized.
2) If a group on AD and DS have members which are local and are
   not synchronized and the members are removed in the group on
   the other side, the delete operation is synchronized and
   deletes all the members including the local members.

Fix description:
1) In windows_generate_update_mods, even if a sync'ed member value
   in a DS entry is not the target of windows sync and it is does
   not exist on DS, a following modify operation including the member
   value is proceeded by confirming the existence on AD.
2) AD->DS: in windows_map_mods_for_replay
   DS->AD: in windwos_generate_update_mods
   added the code to check if an attribute is completely deleted on
   one side, then the each value on the other side is in the sync
   scope or not.  Put the value to the mod for the delete only if
   the value is in the sync scope.

Reviewed by Rich (Thank you!!)

https://fedorahosted.org/389/ticket/415