Incompleteness behaviour for unknown utilities and options

[benozol]

Currently, the behaviour of unknown utilties and options is determined by the command-line option --fail-on-unknown-utilities: By default, the concrete and symbolic interpretation results in an error with a message in stdout. With the option enabled, the interpreter raises exception and fail with return code 7 or 8.

With #60 we can use the failure behaviour, which captures execution outside the coverage of the symbolic execution, for unknown utiltiies and options as well. Consequently, we can discard the option --fail-on-unknow-utilities, and make failure the standard for the concrete interpreter without --real-word.

[Niols]

That has been solved by #114, hasn't it?

[benozol]

Yes!