Servlet 3 implementation.

Servlet 3 implementation.
- Add support for relative fragment ordering and some test cases
- Re-order fragment and annotation processing to match spec
- Implement login/logout
- Provide a method to retrieve the Authenticator in use by a Context
- Add methods to Authenticator interface to facilitate the new login/login methods
- Enable Authenticator.register() to be used for logout as well as login

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@835460 13f79535-47bb-0310-9956-ffa450edef68