#5778 Implement Grob::event_cause, Grob::ultimate_event_cause

[David Kastrup]

Implement Grob::event_cause, Grob::ultimate_event_cause

Those were implemented in Grob_info only previously which does not make a lot of sense,
given that they don't access anything particular to Grob_info.

Also contains commit:

Use Grob::event_cause and Grob::ultimate_event_cause where useful

Frankly, this one has been bugging me on and off for years. I just
had one compilation error too much today.

http://codereview.appspot.com/559500043

[Anonymous]

Passes make. make check and a full make doc

[Anonymous]

Patch on countdown for Feb 24th

[Anonymous]

Patch counted down - please push.

[Jonas Hahnfeld]

commit 7495e987bce4ced7926b641c9119d1e9efce0683
Author:     David Kastrup <dak@gnu.org>
AuthorDate: Thu Feb 20 16:08:17 2020 +0100
Commit:     David Kastrup <dak@gnu.org>
CommitDate: Mon Feb 24 21:35:32 2020 +0100

    Issue 5778/2: Use Grob::event_cause and Grob::ultimate_event_cause where useful

commit bd102efc3768c735b10a79397e11df55c8957818
Author:     David Kastrup <dak@gnu.org>
AuthorDate: Thu Feb 20 15:50:29 2020 +0100
Commit:     David Kastrup <dak@gnu.org>
CommitDate: Mon Feb 24 21:35:32 2020 +0100

    Issue 5778/1: Implement Grob::event_cause, Grob::ultimate_event_cause

    Those were implemented in Grob_info only previously which does not make a lot of sense,
    given that they don't access anything particular to Grob_info.