core: deregister all hooks before leaving pconf, otherwise some late cleanup
or function call (e.g. ap_log) may use one while DSOs are unloaded.

See PR 61558 (double/second fault).


core, MPMs unix: follow up to r1809881.

Deregister all hooks first (in pre_cleanup), by doing it last we could still
have had them run when DSOs were unloaded.

Likewise, avoid double faults when handling fatal signals by restoring the
default handler before pconf is cleared (we can't ap_log_error there).

Finally, we need to ignore sig_term/restart (do nothing) when the main
process is exiting (i.e. ap_pglobal is destroyed), since retained_data are
freed.

Aimed to fix all faults in PR 61558.


MPMs unix: follow up to r1809881 and r1809973.

unset_signals() is called when ap_pglobal is destroyed too.


Follow up to r1809881: CHANGES entry.


Reviewed by: ylavic, jim, covener


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1820794 13f79535-47bb-0310-9956-ffa450edef68