Change the configure-based MPM build mechanism to support building

an MPM as a shared shared or dynamic module, primarily using the
APACHE_MPM_MODULE() function.

--enable-mpms-shared now builds/installs the MPMs as dynamic modules.
(But no LoadModule directives are added.)


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@832434 13f79535-47bb-0310-9956-ffa450edef68