Implemented stateless login for Auth

I think I have finally managed to get stateless auth working in a sensible way with minimal hacking of the AuthComponent.

With this patch when using only BasicAuthenticate there is no redirection to login action nor session starting.

When using Basic and Form authenticators together (order matters) if required http headers are passed and valid user is found it behaves as mentioned above else continues with regular form basic authentication.

For now I only modified existing tests to pass. More tests need to be added after wiser men confirm what I have done is a good idea :smile: