Checking if a given port is installed in pre-fetch

[Rainer Müller]

Daniel J. Luke wrote:
> There's not a built-in way to do this (but it might be a nice base/  
> feature), and I don't know of a really good way of doing it (you could  
> probably check for an installed binary in a pre-fetch action and  
> output an appropriate ui_error message).

Which would issue a warning in tracemode or make it fail at all.

Rainer