Orca Structural Navigation for Links has been added

[Joanmarie Diggs <j-diggs comcast net>]

Hi All.

I have just checked in a change to Gecko.py which adds support for 
structural navigation by link in Firefox.  U is for the next unvisited 
link; Shift+U for the previous unvisited link; V for the next visited 
Link; and Shift V for the (yup, you guessed it) previous visited link. 
<smile>

Take care.
Joanie