Fix distanceOfTimeInWords() failing tests

Improve tests for Mad_Model config parsing.

Overhaul validation factory

Restructure association proxy so that the proxy is always loaded and the
build(), create(), etc. methods hang on the proxy. Data load will then be lazy
on the first call to the proxy iterator/access.

Rework sendFile() so that it passes a stream resource to the response object
and that gets streams out instead of file_get_conents()

Add test for Mad_Test_Functional to ensure that session variables from the
request object get carried over into the response object by _initResponse().

Make $model->logger work on the instance like Rails. Currently it is static
Model::logger()

Add test to verify that timestamps are updated if the attribute is null.

Add test for mad_controller_request_http->getsessionid()

Overhaul session handling. Remove the hack $_SESSION = array() from
Mad_Controller_Base added in changeset 370.