Merge r463427 from trunk:

mod_authnz_ldap: Add an AuthLDAPRemoteUserAttribute directive. If
set, REMOTE_USER will be set to this attribute, rather than the
username supplied by the user. Useful for example when you want users
to log in using an email address, but need to supply a userid instead
to the backend.

Submitted by: minfrin
Reviewed by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@484638 13f79535-47bb-0310-9956-ffa450edef68