--add doesn't seem to work with -loop

[GoogleCodeExporter]

What steps will reproduce the problem?
1. use "loadframes" to load a sequence of images
(ImageStack -loadframes 03289.jpg 03290.jpg 03291.jpg 03292.jpg 03293.jpg 
03294.jpg 03295.jpg 03296.jpg - still can't load more than 8 frames)

2. use -loop 7 --add to add the second to the first 7 times to add the stack 
together. 

3. Stack Underflow.

What is the expected output? What do you see instead?
Trying to use "add" to sum a bunch of images and then wish to divide the pixel 
values by the number of images, but add doesn't seem to want to be used on any 
more than two images.

Maybe I should just use eval?

What version of the product are you using? On what operating system?
win764, latest version of imagestack.

Original issue reported on code.google.com by [email protected] on 15 Feb 2011 at 3:54