[orca-list] improve irssi support

[Tyna Pelletier-Bilodeau <ecole tyna gmail com>]

Hi,
as far as I know the support for irssi (irc client) in orca has been 
like this for at least 2 years from what I can tell:

* orca will read incoming and outgoing messages and the statusbar every 
time a new message appeares, but only if the current window is not yet full
* if you change windows in irssi orca will start reading the window you 
are now in from the top
* in the case where the current window is full, orca will stop reading 
incoming messages and the one you send, or may read the window from the 
top instead
* thanks to the now improved flat review, if you want to read a new 
message you need not to change window and go back on the terminal, but 
still having it read automatically would be nice

As far as I know, all irssi is using is terminfo, I don't know why 
speakup works so well with it and yet orca does not, but I'd like it if 
support could be improved.

* speakup reads incoming and outgoing messages without any issue, same 
for the statusbar. It also does not read the statusbar when you send a 
new message or receive a message when the current window isn't full, 
only on activity (i.e: messages in another window).