Merge r1638879, r1640031 from trunk:

avoid dereferencing a recently apr_pool_clear()'ed event_conn_state_t *cs
in several paths where ptrans is being recycled at the end of a request.



event, eventopt: follow up to r1638879 and r1639960.
Clear the pool in ap_push_pool() before recycling.

Submitted by: covener, ylavic
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1642859 13f79535-47bb-0310-9956-ffa450edef68