unify stack implementations
Graphviz contains a number of inline implementations of a stack data structure:
initStkimplementation duplicated in at least five places
- gxl2gv's ad hoc
I have not analyzed how much these overlap, but I hope we can all agree this is more stack implementations than we would like to maintain. As a first step, de-duplicating all the
initStk copies would be progress. I have not yet investigated which is the best target library to merge them into.