handle an unfortunate implication of loadable MPMs:

calls to ap_mpm_query() must be deferred until after the register-hooks hook, since that's 
where the MPM registers its mpm-query hook


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@761226 13f79535-47bb-0310-9956-ffa450edef68