From what I can tell `CClientUIInterface::[signal_name]_disconnect` is a no-op.

In other words calling it does *not* disconnect the slot:

For example `uiInterface.NotifyBlockTip_disconnect(BlockNotifyGenesisWait);` in `AppInitMain(...)` does not disconnect `BlockNotifyGenesisWait` as one would expect. The result being that `BlockNotifyGenesisWait` is invoked for every new block :-)

Running `bitcoind` with some debug printing added shows the issue:

```
[signals] CClientUIInterface::ThreadSafeMessageBox_connect(...) entered with 0 connected slots.
[signals] CClientUIInterface::ThreadSafeMessageBox_connect(...) exited with 1 connected slots.
[signals] CClientUIInterface::ThreadSafeQuestion_connect(...) entered with 0 connected slots.
[signals] CClientUIInterface::ThreadSafeQuestion_connect(...) exited with 1 connected slots.
[signals] CClientUIInterface::InitMessage_connect(...) entered with 0 connected slots.
[signals] CClientUIInterface::InitMessage_connect(...) exited with 1 connected slots.
[signals] CClientUIInterface::InitMessage_connect(...) entered with 1 connected slots.
[signals] CClientUIInterface::InitMessage_connect(...) exited with 2 connected slots.
[signals] Calling uiInterface.NotifyBlockTip_connect(&RPCNotifyBlockChange) in OnRPCStarted()
[signals] CClientUIInterface::NotifyBlockTip_connect(...) entered with 0 connected slots.
[signals] CClientUIInterface::NotifyBlockTip_connect(...) exited with 1 connected slots.
[signals] Calling uiInterface.NotifyBlockTip_connect(BlockNotifyGenesisWait) in AppInitMain(...)
[signals] CClientUIInterface::NotifyBlockTip_connect(...) entered with 1 connected slots.
[signals] CClientUIInterface::NotifyBlockTip_connect(...) exited with 2 connected slots.
[signals] RPCNotifyBlockChange(...) was invoked.
[signals] BlockNotifyGenesisWait(...) was invoked.
[signals] Calling uiInterface.NotifyBlockTip_disconnect(BlockNotifyGenesisWait) in AppInitMain(...)
[signals] CClientUIInterface::NotifyBlockTip_disconnect(...) entered with 2 connected slots.
[signals] CClientUIInterface::NotifyBlockTip_disconnect(...) exited with 2 connected slots.
[signals] RPCNotifyBlockChange(...) was invoked.
[signals] BlockNotifyGenesisWait(...) was invoked.
[signals] RPCNotifyBlockChange(...) was invoked.
[signals] BlockNotifyGenesisWait(...) was invoked.
[signals] RPCNotifyBlockChange(...) was invoked.
[signals] BlockNotifyGenesisWait(...) was invoked.
... and so on ...
```

Note how `BlockNotifyGenesisWait(...)` is called also after `uiInterface.NotifyBlockTip_disconnect(BlockNotifyGenesisWait)`.

I think the problem is that the `disconnect(...)` member function of `boost::signals2::signal` expects a function pointer to be passed in (the same that was passed to `.connect(...)`), but we're doing:

```
void CClientUIInterface::signal_name##_disconnect(std::function<signal_name##Sig> fn)
{
    return g_ui_signals.signal_name.disconnect(&fn);
}
```
BTN_CANCEL  = 0x00400000U, 
        BTN_DISCARD = 0x00800000U, 
        BTN_HELP    = 0x01000000U, 
        BTN_APPLY   = 0x02000000U, 
        BTN_RESET   = 0x04000000U, 
        /**
         * Mask of all available buttons in CClientUIInterface::MessageBoxFlags
         * This needs to be updated, when buttons are changed there!
         */
        BTN_MASK = (BTN_OK | BTN_YES | BTN_NO | BTN_ABORT | BTN_RETRY | BTN_IGNORE |
                    BTN_CLOSE | BTN_CANCEL | BTN_DISCARD | BTN_HELP | BTN_APPLY | BTN_RESET),
        
        MODAL               = 0x10000000U,
        
        SECURE              = 0x40000000U,
        
        MSG_INFORMATION = ICON_INFORMATION,
        MSG_WARNING = (ICON_WARNING | BTN_OK | MODAL),
        MSG_ERROR = (ICON_ERROR | BTN_OK | MODAL)
    };
#define ADD_SIGNALS_DECL_WRAPPER(signal_name, rtype, ...)                                  \
    rtype signal_name(__VA_ARGS__);                                                        \
    using signal_name##Sig = rtype(__VA_ARGS__);                                           \
    boost::signals2::connection signal_name##_connect(std::function<signal_name##Sig> fn); \
    void signal_name##_disconnect(std::function<signal_name##Sig> fn);
    
    ADD_SIGNALS_DECL_WRAPPER(ThreadSafeMessageBox, bool, const std::string& message, const std::string& caption, unsigned int style);
    
    ADD_SIGNALS_DECL_WRAPPER(ThreadSafeQuestion, bool, const std::string& message, const std::string& noninteractive_message, const std::string& caption, unsigned int style);