message: Change ScriptPubKeyMan::Upgrade to default to return true
  If a ScriptPubKeyMan does not implement Upgrade, then using upgraewallet
  will fail unexpectedly. By changing the default to return true, then
  this error can be avoided. This is still correct because a successful
  upgrade can be that nothing happened.
diff: @@ -207,7 +207,7 @@ public:
  virtual bool CanGetAddresses(bool internal = false) const { return false; }
  /** Upgrades the wallet to the specified version */
  - virtual bool Upgrade(int prev_version, int new_version, bilingual_str& error) { return false; }
  + virtual bool Upgrade(int prev_version, int new_version, bilingual_str& error) { return true; }
  virtual bool HavePrivateKeys() const { return false; }
  