update the mpm_common docs to deal with multiple meanings for the same directives.
In the future, it would be a wise idea not to use the same directive name as
another MPM unless the directive really does exactly the same thing in both
MPMs.
Problem pointed out by: Rich Bowen
git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@95663 13f79535-47bb-0310-9956-ffa450edef68
