Add ap_mpm_is_experimental and ap_mpm_is_threaded. Use these instead of...

Add ap_mpm_is_experimental and ap_mpm_is_threaded.  Use these instead of checking for specific MPMs.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@156574 13f79535-47bb-0310-9956-ffa450edef68