Merge r1821624, r1821625, r1821626, r1821627, r1821629, r1821632, r1821635, r1821639...

Shared fdqueue code between MPMs event and worker into mpm_fdqueue.

This first step moves the files server/mpm/event/fdqueue.[ch] to
server/mpm_fdqueue.[ch] (untouched for now, simple svn move).

Will follow up with the necessary changes to mpm_unix.* for common code.

mpm_fdqueue: follow up to r1821624.

And now it's mpm_fdqueue, with minimal #includes.

mpm_fdqueue: follow up to r1821624.

Opacify fdqueue types.

mpm_fdqueue: follow up to r1821624.

Style, no functional change.

mpm_fdqueue: follow up to r1821624.

Rename ap_queue_info_get_idlers() to ap_queue_info_num_idlers().

mpm_fdqueue: follow up to r1821624.

Clear recycled_pools_count in ap_free_idle_pools().

mpm_fdqueue: follow up to r1821624.

Prepare mpm_worker to use common fdqueue.

mpm_worker: follow up to r1821624.

Use common [mpm_]fdqueue.

mpm_fdqueue: follow up to r1821624.

The implemention wants APR_HAS_THREADS too.

mpm_fdqueue: follow up to r1821624.

The code is not part of the API.

mpm_fdqueue: follow up to r1821624.

Fix typo in comment.

mpm_fdqueue: follow up to r1821624.

Cosmetics, 80 cols, no functional change.

mpm_worker: follow up to r1821624.

Free idle pools while stopping.

mpm_fdqueue: follow up to r1821624.

Be explicit in the naming about what's push/pop-ed.

mpm_fdqueue: follow up to r1821624.

Either error matters, simplify code.

mpm_fdqueue: follow up to r1821624.

Make the allocation and zero-ing in ap_queue_init() => ap_queue_create().

mpm_fdqueue: follow up to r1821624.

Export ap_queue_*() fonctions, so that they are accessible from MPMs, but
don't provide "mpm_fdqueue.h" in the API (include/).

mpm_fdqueue: follow up to r1821624.

80 colums.

Follow up to r1821624: CHANGES entry.

Submitted by: ylavic
Reviewed by: ylavic, minfrin, jim

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1824866 13f79535-47bb-0310-9956-ffa450edef68