Fixed ClassFilterAwareUnionMethodMatcher equals implementation

Issue: SPR-10604
(cherry picked from commit f329140)
DelegatingFilterProxy avoids synchronization for pre-resolved delegate

Issue: SPR-10413
(cherry picked from commit c26272c)
Restored overridable getXStream() method in Spring Framework 3.2.x

Also setting the bean class loader on the XStream instance itself now.

Issue: SPR-10421