clean up the scoreboard properly after threaded processes die gracefully.

find_child_by_pid() failed to do its job, because ap_max_daemons_used was
too low.  There was some recent breakage in threaded that contributes to
the problem.

However, find_child_by_pid() should not be using the current number of
daemons.  It could have been recently reduced, which makes it fail to
find the exiting process.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@90015 13f79535-47bb-0310-9956-ffa450edef68