Two callers of get_spendable_coins were removing frozen addrs
before calling. Put that functionality in the function.
We shouldn't be able to send_from a frozen address. This was
possible in the current release because logic assumed a two-element
tuple was returned when it is now three-element. Fix that too.
Command line options listunspent and createrawtransaction currently
ignore frozen addresses. I'm not sure that's right but I've preserved
that behaviour.
With this patch only the wallet class refers to self.frozen_addresses;
other clients use is_frozen() now.
320f9a3790