Fix a couple of new MSVC 2010 warnings

Compiler complains because in Book we have a d'tor but not
copy c'tor and assignement operator (warning C4511 and C4512),
note that after adding them (just declared) you now need also
default c'tor !

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/book.h

@@ -53,7 +53,10 @@ struct BookEntry {
 };
 
 class Book : private std::ifstream {
+  Book(const Book&); // just decleared..
+  Book& operator=(const Book&); // ..to avoid a warning
 public:
+  Book() {}
   ~Book();
   void open(const std::string& fName);
   void close();