Work with SpringSessionSynchronization changes from Spring 4.1.0.RC2 

In Spring 4.1.0.RC2, the SpringSessionSynchronization constructor changed. See https://jira.spring.io/browse/SPR-9020

This commit ensures compatibility with Spring before 4.1.0.RC2 and after 4.1.0.RC2.
Merge pull request #33 from candrews/patch-4

Work with SpringSessionSynchronization changes from Spring 4.1.0.RC2