[orca-list] Added customization to disable dead accessible event filter

[Joanmarie Diggs <jdiggs igalia com>]

Hey all.

Those of you who have Thunderbird folders with large amounts of messages
have reported problems using Thunderbird, citing commits that filter out
events from dead accessible objects.

Thunderbird going non responsive is either a Thunderbird bug, an AT-SPI2
bug, or both, as I've stated in previous messages. See, in particular:

* https://bugzilla.mozilla.org/show_bug.cgi?id=924915
* https://bugzilla.gnome.org/show_bug.cgi?id=650090

In addition, others of you have reported that this filter has made
things more performant for you. So I really don't want to remove the filter.

Taking all of this into account, I have just committed a change to
master that makes it possible for you to disable the dead accessible
event checking and filter. I hope that this solution will solve the
Thunderbird issue for you. Those of you with the Thunderbird problems
should put the following into your orca-customizations.py:

import orca.settings
settings.disableDeadAccessibleFilter = True

Please let me know if that helps. Thanks!
--joanie