Authentication takes a while when used with LDAP

Fix committed to redback trunk in -r1371:

• cache ldap users and ldap connection, expiry is 10mins and 5mins, respectively
• during authn, check cache first and only go to the ldap server if user isn't found in the cache
• added tests

Shorten the TTL of ldap connections and ldap users cache to 15secs and 2mins, respectively in commit -r1372.

Removed redundant call to ldap when getting ldap user for the security session in -r1373. Fix submitted by Jevica Zurbano. Thanks!

Additional changes made in -r1374:

• removed caching of ldap connections, cache userDn instead to minimize lookups to ldap server during authentication
• adjusted TTL of ldap users and ldap userDn cache, set both to 3mins.
• updated tests
• also set ldap connection pooling when using Sun's ldap context factory

Set timeout to 3600 for ldap connection pooling in -r1375.

Merged above fixes to 1.3-Mx branch in -r1376. I had to change the implementation of LdapCacheService to manage the caches directly because the CacheBuilder in spring-cache isn't compatible with the 1.3-Mx branch. The branch is using 2.5.x spring while spring-cache is using 3.0.x