Cleanup (reduce eclipse warnings, no functional changes)

- Updated httpcore, to be able to use EntityUtils.consume() to get rid of
  deprecation warnings
Move contextHasFormBasedSecurityConstraint to SessionManager.

- No need for MemcachedSessionService specializations anymore
- Simplifies HibernateCollectionsTest
Fix testSessionCreatedForContainerProtectedResourceIsStoredInMemcached

Tomcat8 now redirects with 303 instead of 302. For 303 httpclient automatically
redirects, so httpclient must be asked not to do so, additionally the status code
checks in TestUtils needed to be extended for 303.