Fixed some bugs picked up in flake8

pycmx/channel_map.py

@@ -98,8 +98,8 @@ class ChannelMap:
                 self.set_audio_channel(int( matchresult.group(1)), True )
 
     def _append_ext(self, audio_ext):
-        self.a3 = ext.audio3
-        self.a4 = ext.audio4
+        self.a3 = audio_ext.audio3
+        self.a4 = audio_ext.audio4
 
     def __or__(self, other):
         """

pycmx/transition.py

@@ -70,12 +70,12 @@ class Transition:
     @property
     def key_background(self):
         "`True` if this edit is a key background."
-        return self.transition == KeyBackground
+        return self.transition == Transition.KeyBackground
 
     @property
     def key_foreground(self):
         "`True` if this edit is a key foreground."
-        return self.transition == Key
+        return self.transition == Transition.Key
 
     @property
     def key_out(self):
@@ -83,4 +83,4 @@ class Transition:
         `True` if this edit is a key out. This material will removed from
         the key foreground and replaced with the key background.
         """
-        return self.transition == KeyOut
+        return self.transition == Transition.KeyOut