Avoid scoped_connection compile error with boost 1.55.0

Construct scoped_connection directly instead of relying on copy initialization
and move constructor. Avoids the following compile error in debian jessie:

```
In file included from /usr/include/boost/signals2/signal.hpp:21:0,
                 from ./util.h:29,
                 from ./dbwrapper.h:11,
                 from ./txdb.h:10,
                 from ./test/test_bitcoin.h:11,
                 from qt/test/wallettests.cpp:11:
/usr/include/boost/signals2/connection.hpp: In function ‘uint256 {anonymous}::SendCoins(CWallet&, SendCoinsDialog&, const CBitcoinAddress&, CAmount)’:
/usr/include/boost/signals2/connection.hpp:234:7: error: ‘boost::signals2::scoped_connection::scoped_connection(const boost::signals2::scoped_connection&)’ is private
       scoped_connection(const scoped_connection &other);
       ^
qt/test/wallettests.cpp:47:6: error: within this context
     });
      ^
```

Error reported by Pavel Janík <Pavel@Janik.cz> in
https://github.com/bitcoin/bitcoin/pull/9974#issuecomment-287550034

0 files changed, 0 insertions, 0 deletions