poor error message

[Anniepoo]

Failing static sandbox safety analysis is a common enough occurance that it deserves a better error message than the obscure

Arguments are not sufficiently instantiated
Reachable from:
'$swish wrapper'(A,B)

Can we have the print_message system detect this specific case and put a well worded English warning?

See

SWI-Prolog/packages-pengines#29

Something like
"We're unable to execute your query because we're not sure it won't harm the server. For example, if you queried halt, you would stop the server. Sometimes perfectly innocent queries do this, and our system's just not smart enough to know they're safe."