worker MPM/mod_status: Support per-worker tracking of pid and

worker MPM/mod_status: Support per-worker tracking of pid and
generation in the scoreboard so that mod_status can accurately
represent workers in processes which are gracefully terminating.

New child processes with worker MPM can take over slots of
individual threads within gracefully terminating processes.
Sometimes this is a problem (too many of these gracefully
terminating processes), so it is helpful to have mod_status
provide the information required to recognize these processes.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@156274 13f79535-47bb-0310-9956-ffa450edef68