Use all available scoreboard slots

Allow to use all slots up to ServerLimit. This makes 'scoreboard full'
errors much less likely.

And if ther is a situation where the scoreboard is full, don't make any
more processes finish gracefully due to reduced load until some old
processes have terminated. Otherwise, the situation would get worse once
the load increases again.

ap_daemon_limit is renamed to the more descriptive active_server_limit,
to make sure that all its uses are taken care of.

PR 53555



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1770752 13f79535-47bb-0310-9956-ffa450edef68