Better support for USB devices

Benefits of this rewrite include:

- support of disconnecting / reconnecting a device without having
  to close the wallet, even in a different USB socket
- support of multiple keepkey / trezor devices, both during wallet
  creation and general use
- wallet is watching-only dynamically according to whether the
  associated device is currently plugged in or not

plugins/trezor/client.py

@@ -27,7 +27,7 @@ class GuiMixin(object):
         else:
             cancel_callback = None
 
-        self.handler.show_message(message % self.device, cancel_callback)
+        self.handler().show_message(message % self.device, cancel_callback)
         return self.proto.ButtonAck()
 
     def callback_PinMatrixRequest(self, msg):
@@ -40,14 +40,14 @@ class GuiMixin(object):
                      "Note the numbers have been shuffled!"))
         else:
             msg = _("Please enter %s PIN")
-        pin = self.handler.get_pin(msg % self.device)
+        pin = self.handler().get_pin(msg % self.device)
         if not pin:
             return self.proto.Cancel()
         return self.proto.PinMatrixAck(pin=pin)
 
     def callback_PassphraseRequest(self, req):
         msg = _("Please enter your %s passphrase")
-        passphrase = self.handler.get_passphrase(msg % self.device)
+        passphrase = self.handler().get_passphrase(msg % self.device)
         if passphrase is None:
             return self.proto.Cancel()
         return self.proto.PassphraseAck(passphrase=passphrase)
@@ -65,18 +65,29 @@ def trezor_client_class(protocol_mixin, base_client, proto):
 
     class TrezorClient(protocol_mixin, GuiMixin, base_client, PrintError):
 
-        def __init__(self, transport, plugin):
+        def __init__(self, transport, path, plugin):
             base_client.__init__(self, transport)
             protocol_mixin.__init__(self, transport)
             self.proto = proto
             self.device = plugin.device
-            self.handler = None
+            self.path = path
+            self.wallet = None
             self.plugin = plugin
             self.tx_api = plugin
-            self.bad = False
             self.msg_code_override = None
-            self.proper_device = False
-            self.checked_device = False
+
+        def __str__(self):
+            return "%s/%s/%s" % (self.label(), self.device_id(), self.path[0])
+
+        def label(self):
+            return self.features.label
+
+        def device_id(self):
+            return self.features.device_id
+
+        def handler(self):
+            assert self.wallet and self.wallet.handler
+            return self.wallet.handler
 
         # Copied from trezorlib/client.py as there it is not static, sigh
         @staticmethod
@@ -94,34 +105,8 @@ def trezor_client_class(protocol_mixin, base_client, proto):
                 path.append(abs(int(x)) | prime)
             return path
 
-        def check_proper_device(self, wallet):
-            try:
-                self.ping('t')
-            except BaseException as e:
-                self.plugin.give_error(
-                    __("%s device not detected.  Continuing in watching-only "
-                       "mode.") % self.device + "\n\n" + str(e))
-            if not self.is_proper_device(wallet):
-                self.plugin.give_error(_('Wrong device or password'))
-
-        def is_proper_device(self, wallet):
-            if not self.checked_device:
-                addresses = wallet.addresses(False)
-                if not addresses:   # Wallet being created?
-                    return True
-
-                address = addresses[0]
-                address_id = wallet.address_id(address)
-                path = self.expand_path(address_id)
-                self.checked_device = True
-                try:
-                    device_address = self.get_address('Bitcoin', path)
-                    self.proper_device = (device_address == address)
-                except:
-                    self.proper_device = False
-                wallet.proper_device = self.proper_device
-
-            return self.proper_device
+        def address_from_derivation(self, derivation):
+            return self.get_address('Bitcoin', self.expand_path(derivation))
 
         def change_label(self, label):
             self.msg_code_override = 'label'
@@ -144,12 +129,26 @@ def trezor_client_class(protocol_mixin, base_client, proto):
         def atleast_version(self, major, minor=0, patch=0):
             return cmp(self.firmware_version(), (major, minor, patch))
 
-        def call_raw(self, msg):
-            try:
-                return base_client.call_raw(self, msg)
-            except:
-                self.print_error("Marking %s client bad" % self.device)
-                self.bad = True
-                raise
 
-    return TrezorClient
+    def wrapper(func):
+        '''Wrap base class methods to show exceptions and clear
+        any dialog box it opened.'''
+
+        def wrapped(self, *args, **kwargs):
+            handler = self.handler()
+            try:
+                return func(self, *args, **kwargs)
+            except BaseException as e:
+                handler.show_error(str(e))
+                raise e
+            finally:
+                handler.finished()
+
+        return wrapped
+
+    cls = TrezorClient
+    for method in ['apply_settings', 'change_pin', 'get_address',
+                   'get_public_node', 'sign_message', 'sign_tx']:
+        setattr(cls, method, wrapper(getattr(cls, method)))
+
+    return cls