Exchange

Change log:
- dropdownlist for books to exchange now display only books that can be
exchanged
Merge remote-tracking branch 'origin/master'

Conflicts:
	BookExchange/App_Data/BookExchange.mdf
	BookExchange/App_Data/BookExchange_log.ldf
	BookExchange/BookExchange.sln
	BookExchange/BookExchange.v11.suo
	BookExchange/vwd.webinfo