Type-errors in modules imported in REPL could lead to infinite loop

[ppolesiuk]

The buggy behavior can be reproduced, by the two following files.
Good.dbl:

(* empty *)

Bad.dbl:

import Good
// some type error:
let _ = () ()

When in REPL we import bad, we would fall into infinite loop.

> import Bad ;;
./Bad.dbl:3:9-10: fatal error: This expression has type Unit. It is not a function and cannot be applied
./Bad.dbl:3:9-10: fatal error: This expression has type Unit. It is not a function and cannot be applied
./Bad.dbl:3:9-10: fatal error: This expression has type Unit. It is not a function and cannot be applied
...

As suggested by @forell in #80, resolving the issue #82 could help to fix this bug.