changed for-loop in graph_find_edge. iterates now over pointer.
changed all for-loops in gt_scaffolder_graph_filtering to iterate directly over pointer
changed first for loop in gt_scaffolder_graph_makescaffold to iterate over pointer directly. negated if-condition and deleted continue.
changed the last for-loops in gt_scaffolder_graph_makescaffold to iterate over pointer directly
defined new function to check and mark polymorphic vertices.
Merge branch 'master' of https://github.com/dorleosterode/gt-scaffold