Check for instance multiplicity from SCCs for a graph and call-graph

[mchalupa]

Single instance = not on loop, not in recursive or repeated call. In invalidated pta, we now do it very imprecisely. Do it better. For PTA, it partially depends on #241. For RD, we can go ahead, but must compute SCC first for each graph (so we want single graphs too...).

[mchalupa]

WIP in pta-impr