Convert some old-style string exceptions to class exceptions.
diff --git a/Lib/aifc.py b/Lib/aifc.py
index e00b23f..f709d88 100644
--- a/Lib/aifc.py
+++ b/Lib/aifc.py
@@ -137,7 +137,8 @@
 import struct
 import __builtin__
 
-Error = 'aifc.Error'
+class Error(Exception):
+    pass
 
 _AIFC_version = 0xA2805140      # Version 1 of AIFF-C