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

Patch and tests by Brian Harring, with improvements by Ralf Schmitt.
diff --git a/Misc/NEWS b/Misc/NEWS
index cb0e19d..76bf481 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -10,6 +10,9 @@
 Core and Builtins
 -----------------
 
+- Issue #1574217: isinstance now catches only AttributeError, rather than
+  masking all errors.
+
 - Issue #10391: Don't dereference invalid memory in error messages in the ast
   module.