Optimization... for large slotmems, it would be useful to know

which ones are actually "in use"... So flag this. Need a way
to de-allocate a slot for completeness I think, but am having
a hard time coming up with a use case...



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@774036 13f79535-47bb-0310-9956-ffa450edef68