I think I had found an answer to this, but I cannot get my hand
on it, so here it is:
I forced the install of graph-tool package
Now it is of course tagged as broken, so update manager wont do anything.
But I want to accept it, I know it is not really broken.
(In fact, graph-tool_xxx.deb asks for libcgal4.
squeeze only has libcgal5, so I am betting this is not an issue,
as far as graph-tool is concerned.)
Thanks every one.