Learn why nogofunc sanity check is triggered

[kalexmills]

A sanity check added to nogofunc is being triggered, which, for me, is calling into question the accuracy of some of the callgraph procedures.

Based on the symptoms, I suspect one of these:

1. the callgraph reversal in lazyInitCalledBy is wrong
2. nogofunc is wrong
3. the CalledByGraphBFS is wrong
4. nothing is wrong and I shouldn't expect a BFS finding a path in one direction to also find the same path in the reverse graph (unlikely).

[kalexmills]

I'm thinking this is actually what happens when a third-party function is reached, so it should have been modified by the most recent changes. I need to convince myself via reading the code. Putting a note here for later.

[kalexmills]

Closing in favor of #78.