Merge r1572896, r1572911, r1603156 from trunk:

Merge r1572896, r1572911, r1603156 from trunk:

mod_deflate:
Don't fail when asked to flush inflated data to the user-agent and that
coincides with the end of stream ("Zlib error flushing inflate buffer").
PR 56196.

Submitted By: [Christoph Fausak <christoph.fausak glueckkanja com>]
Committed By: ylavic

mod_deflate: follows up r1572896.
Be safe from successive or post end-of-stream flush buckets.

Add missing CHANGES entries for r1572655,1572663,1572668-1572671,1573224,1586745,1587594,1587639,1590509, r1572092, and r1572896,1572911.
Submitted by: ylavic
Reviewed/backported by: jim

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@1611428 13f79535-47bb-0310-9956-ffa450edef68