Fix connected component calculation to use explicit stack rather than recursion in order to handle big graphs.
Fix connected component calculation to use explicit stack rather
than recursion in order to handle big graphs.

We already have a fair amount of bug reports where recursion has
blown the stack.

pixelglow/graphviz,pixelglow/graphviz,MjAbuz/graphviz,BMJHayward/graphviz,MjAbuz/graphviz,jho1965us/graphviz,tkelman/graphviz,tkelman/graphviz,jho1965us/graphviz,ellson/graphviz,ellson/graphviz,jho1965us/graphviz,tkelman/graphviz,jho1965us/graphviz,kbrock/graphviz,kbrock/graphviz,tkelman/graphviz,tkelman/graphviz,tkelman/graphviz,ellson/graphviz,ellson/graphviz,MjAbuz/graphviz,MjAbuz/graphviz,tkelman/graphviz,ellson/graphviz,pixelglow/graphviz,ellson/graphviz,kbrock/graphviz,BMJHayward/graphviz,ellson/graphviz,ellson/graphviz,jho1965us/graphviz,MjAbuz/graphviz,pixelglow/graphviz,tkelman/graphviz,BMJHayward/graphviz,BMJHayward/graphviz,ellson/graphviz,MjAbuz/graphviz,tkelman/graphviz,kbrock/graphviz,pixelglow/graphviz,BMJHayward/graphviz,MjAbuz/graphviz,pixelglow/graphviz,tkelman/graphviz,kbrock/graphviz,pixelglow/graphviz,MjAbuz/graphviz,jho1965us/graphviz,kbrock/graphviz,kbrock/graphviz,jho1965us/graphviz,pixelglow/graphviz,BMJHayward/graphviz,BMJHayward/graphviz,jho1965us/graphviz,tkelman/graphviz,BMJHayward/graphviz,ellson/graphviz,jho1965us/graphviz,pixelglow/graphviz,BMJHayward/graphviz,MjAbuz/graphviz,BMJHayward/graphviz,kbrock/graphviz,BMJHayward/graphviz,jho1965us/graphviz,kbrock/graphviz,pixelglow/graphviz,ellson/graphviz,jho1965us/graphviz,pixelglow/graphviz,kbrock/graphviz,MjAbuz/graphviz,kbrock/graphviz,MjAbuz/graphviz