Convert some old-style string exceptions to class exceptions.
diff --git a/Lib/test/test_rgbimg.py b/Lib/test/test_rgbimg.py
index 38bcdf5..1fa201d 100644
--- a/Lib/test/test_rgbimg.py
+++ b/Lib/test/test_rgbimg.py
@@ -4,7 +4,8 @@
 
 from test_support import verbose, unlink, findfile
 
-error = 'test_rgbimg.error'
+class error(Exception):
+        pass
 
 print 'RGBimg test suite:'