Convert some old-style string exceptions to class exceptions.
diff --git a/Lib/toaiff.py b/Lib/toaiff.py
index 84a7786..52c5a89 100644
--- a/Lib/toaiff.py
+++ b/Lib/toaiff.py
@@ -53,7 +53,8 @@
 uncompress.append('uncompress', '--')
 
 
-error = 'toaiff.error' # Exception
+class error(Exception):
+        pass
 
 def toaiff(filename):
 	temps = []