mod_status: note stopping procs in async info table

* add new column "stopping", denoting if a process is shutting down
* add additional "(old gen)", if a process is from before a graceful reload
* add counts of processes and stopping processes to summary line



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1757029 13f79535-47bb-0310-9956-ffa450edef68