Create better logic for showing generation progress

[GoogleCodeExporter]

Right now, we just show a generic progress bar scrolling while we generate
an image.  Previously, we used a fixed-number of images that we planned on
retrieving to report progress.  Neither of these is optimal.  We should
have some sort of call to each plugin to get our "expected" number of
returned images, and show progress based on that.

Original issue reported on code.google.com by swegn...@gmail.com on 12 Mar 2008 at 6:58