Convert some old-style string exceptions to class exceptions.
diff --git a/Lib/wave.py b/Lib/wave.py
index 60c0b98..c8cf997 100644
--- a/Lib/wave.py
+++ b/Lib/wave.py
@@ -73,7 +73,8 @@
 
 import __builtin__
 
-Error = 'wave.Error'
+class Error(Exception):
+    pass
 
 WAVE_FORMAT_PCM = 0x0001