Reverted r576 as it caused a regression.

src/execution.cc

Index: src/execution.cc
===================================================================
--- src/execution.cc	(revision 576)
+++ src/execution.cc	(working copy)
@@ -91,10 +91,12 @@
   value->Verify();
 #endif
 
-  // Update the pending exception and external caught flag and return the value.
+  // Update the pending exception flag and return the value.
   *has_pending_exception = value->IsException();
   ASSERT(*has_pending_exception == Top::has_pending_exception());
-  Top::propagate_external_caught();
+  if (*has_pending_exception) {
+    Top::setup_external_caught();
+  }
 
   // If the pending exception is OutOfMemoryException set out_of_memory in
   // the global context.  Note: We have to mark the global context here