Randomized dfs

[polgreen]

Introduce randomized DFS search.

I have used the command line option --randomized in combination with --dfs, because in a future pull request I also use this to randomize a shortest path based search heuristic

[polgreen]

I assume symex is dead since these PRs have sat here for 2 years without anyone noticing and the master branch fails all CI? If that's the case I won't bother rebasing

@kroening ?

[martin-cs]

I think symex may be dead. Most of the symex-like functionality is now in CBMC which (thanks to @karkhaz @tautschnig @peterschrammel ) can do per-path analysis.

[polgreen]

RIP symex. I won't re-implement these PRs for the per-path analysis though, since I was the sole user and I'm no longer using it. The ideas behind them weren't that novel, so the only thing lost if these die is coding effort.

[karkhaz]

However, the depth-first search mode in CBMC isn't randomized, it's just a standard DFS. Implementing a randomized version shouldn't be very difficult, though. Happy to help if anyone still needs this feature.

[polgreen]

Whoops, sorry Khareem, posted at the same time.