#1574217: only swallow AttributeErrors in isinstance, not everything.

Patch and tests by Brian Harring, with improvements by Ralf Schmitt.
diff --git a/Misc/ACKS b/Misc/ACKS
index 3cb3a29..9c003e9 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -337,6 +337,7 @@
 Lynda Hardman
 Derek Harland
 Jason Harper
+Brian Harring
 Larry Hastings
 Shane Hathaway
 Rycharde Hawkes