Issue #2534: speed up isinstance() and issubclass() by 50-70%, so as to match Python 2.5 speed despite the __instancecheck__ / __subclasscheck__ mechanism. In the process, fix a bug where isinstance() and issubclass(), when given a tuple of classes as second argument, were looking up __instancecheck__ / __subclasscheck__ on the tuple rather than on each type object. Reviewed by Benjamin Peterson and Raymond Hettinger.

--- a/Python/errors.c	Tue Aug 26 17:08:40 2008 +0000
+++ b/Python/errors.c	Tue Aug 26 22:42:08 2008 +0000
@@ -113,7 +113,6 @@
 		/* This function must not fail, so print the error here */
 		if (res == -1) {
 			PyErr_WriteUnraisable(err);
-			/* issubclass did not succeed */
 			res = 0;
 		}
 		PyErr_Restore(exception, value, tb);