Merge r1739008, r1739146, r1739151, r1739193 from trunk:

scoreboard/status: Keep previous worker connection/request data when idle as
prior to 2.4.20.


scoreboard/status: follow up to r1739008.
Restore (completely) pre-2.4.20 behaviour w.r.t. preserved values.
r1739008 was still unnessessarily blanking some values for the time of
BUSY_READ -> BUSY_WRITE (with blocking MPMs).


scoreboard/status: follow up to 1739146.
Comment not needed anymore...


Clarify CHANGES entry, including the correct version for the
restored behaviour.

Submitted by: ylavic
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1741240 13f79535-47bb-0310-9956-ffa450edef68