Makes the SSL provider implementation used to support LDAP communication over SSL configurable

The LDAP authenticator use sun's SSL provider implementation to support LDAP communication via SSL. This is only available in sun official JVM and throw a NoClassDefFoundError in Open Source implementation of JVM or IBM JVM for example.

As Marini Marco pointed out in a mail (see http://markmail.org/message/6cnwalbpk4cdykql) this can be fixed by making SSL provider to use configurable.

We can also found another implementation which we package in the war as dependency.