Merge of r1861338,1862475,1862583,1862865,1863221,1863276 from trunk:
*) mod_http2: core setting "LimitRequestFieldSize" is not additionally checked on merged header fields, just as HTTP/1.1 does. [Stefan Eissing, Michael Kaufmann]
*) mod_http2: fixed a bug that prevented proper stream cleanup when connection throttling was in place. Stream resets by clients on streams initiated by them are counted as possible trigger for throttling. [Stefan Eissing]
*) mod_http2/mpm_event: Fixes the behaviour when a HTTP/2 connection has nothing more to write with streams ongoing (flow control block). The timeout waiting for the client to send WINODW_UPDATE was incorrectly KeepAliveTimeout and not Timeout as it should be. Fixes PR 63534. [Yann Ylavic, Stefan Eissing]
MPMs unix: bind the bucket number of each child to its slot number
We need not remember each child's bucket number in SHM for restarts, for the lifetime of the httpd main process the bucket number can be bound to the slot number such that: bucket = slot % num_buckets.
This both simplifies the logic and helps children maintenance per bucket in threaded MPMs, where previously perform_idle_server_maintenance() could create or kill children processes for the buckets it was not in charge of.