Added a cache to tranbsaction manager lookup to alleiviate locking issue...

...s when we have more than one transaction manager present in application.

I am very interested in this patch and therefore rebasing https://github.com/serioussam/spring-framework/commit/24a3899cc119417f088b32a61acec96d5724d5ea from @serioussam on top of master.

Please let me know if I can help in any way.

Thanks,