Add the ap_get_max_daemons to dexter, prefork and spmt_os2 MPM's. The only

one now lacking it is winnt, but that'll need someone form the winnt camp
to sort out.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@85652 13f79535-47bb-0310-9956-ffa450edef68