Longdesc testing in Linux

I was excited to hear that support for longdesc was added to Orca [1].  I
performed some tests and have the following to report:

* Orca will announce “has description” after it reads the alt attribute
value for an image with a longdesc attribute.  As joanie notes [1], the
user can then invoke the context sensitive menu and choose “View
description” to visit the URL referenced in the longdesc attribute.
* When inspecting Firefox, Accerciser reports that an Action “showlongdesc"
is available.  Clicking the “Perform action” button in Accerciser will open
the URL referenced in the longdesc attribute in another browser tab.

A screenshot that illustrates the above is available here:
https://dl.dropboxusercontent.com/1/view/nsjj327vb8yq4gq/Captured/KpESR.png

Steps to reproduce:

* downloaded, configured and installed the latest version of Orca [2]
3.13.91pre from the master branch
* visited a test page from the longdesc-tests repo [3]
* navigate to image with Orca turned on
* inspect with Accerciser

Special thanks to Joanmarie Diggs for her work maintaining Orca and for
adding support for longdesc.

 [1] https://mail.gnome.org/archives/orca-list/2014-August/msg00327.html
[2] https://git.gnome.org/browse/orca
https://git.gnome.org/browse/orca
[3]
https://rawgit.com/chaals/longdesc-tests/master/external-image-external-description-girt-by-spaces.html

Mark