Use interfaces::Node object instead.
There is a minor change in behavior in this commit, because the new code calls
InterruptRPC() and StopRPC() when previous code did not do this. But this
should be a good thing since it makes sense to interrupt RPC when the system is
shutting down, and it is better for the GUI shut down in a consistent way
regardless of how the shutdown is triggered.
- prevents unsafe shutdowns on Windows, which is known to be
able to cause problems with wallet.dat
- if a users ends a Windows session, this will initiate a client shutdown
and show a Windows dialog, that tells the user what is going on (for
Windows Vista and higher it will even show a reason for blocking the
Windows session end)
