[BZ#416387] Compare differently-named files across directories

Submitted by Joachim Noreiko

Description

I open a directory comparison. There's a 'compare' button in the toolbar, so I assume I can compare files that I suspect may be similar but have different filenames:

Dir A Dir B foo.txt foo2.txt

But I can't select them both at the same time. Selecting in one pane loses the selection in the other.