Implement REQ_ATTRIBUTE using request rec environment table,

so we can use standard SetEnv directive for that.
The ajp specific attributes has to be prefixed using 'AJP_', and are passed
withouth that prefix to the backend.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@104788 13f79535-47bb-0310-9956-ffa450edef68