ISPN-4357 Use a specific cache for managing protofiles

Also upgrade to protobuf-2.6.0 and protostream-2.0.0.Alpha3

Jira: https://issues.jboss.org/browse/ISPN-4357
        https://issues.jboss.org/browse/ISPN-4756
Right, I'll simplify this by removing the synchronization and volatile. Lazy init was needed because in an older version of this code I was also defining the configuration if needed, but now this is done at init.