Bug 3387 - WITHDRAWN items shouldn't check in

Bug 3387 - WITHDRAWN items shouldn't check in

Adds a system preference BlockReturnOfWithdrawnItems to control
whether or not Koha should allow a withdrawn item to be returned
or not.

Also fixes the behavior where Koha will attempt to use a withdrawn
item to fill a hold.

Test Plan:
1) Set BlockReturnOfWithdrawnItems to "Block" ( this is the default )
2) Check an item out to a patron
3) Mark item as withdrawn
4) Attempt to return the item, you should still see the item on the
   borrower's record
5) Set BlockReturnOfWithdrawnItems to "Don't Block"
6) Attempt to return the item, you should see the item is no longer
   on the borrower's record.

Signed-off-by: Owen Leonard <oleonard@myacpl.org>