[texinfo-pretest] Directory for bitmaps

[Karl Berry]

    If the HTML documentation is also installed, the images are as
    separate files anyway.

Sure, but the HTML could be getting served from a totally different
machine, not to mention directory.  So the chances of sharing images
between info and html seem remote to me.  I mean, a particular admin
could set it up at a particular site -- maybe you've done it for
lilypond -- but it's nothing that we could make work by default.

Still, it's definitely easier to look in another directory than to embed
the images, you're right about that.  So maybe that's the way to go
first.