Misleading compiler error message when `fn` is not found for `std::core` module

[alexveden]

Hopefully, sometime we will get test::

So what I found, when calling wrong name (valid is test::equal):

    test::equals(1, 0);

I got:

10:     test::equals(1, 0);
        ^^^^
Error: No 'test' module was imported, did you type it right?

Expected to see something:

 Error: 'test::equals' could not be found, did you perhaps want 'test::equal?

Related to #1779

[lerno]

You currently get the following: 'equals' could not be found, try importing the 'test' module. If I import std I get Error: 'equals' could not be found in std::core::test.

Is that good enough?

[lerno]

I'll assume the answer is "yes" otherwise reopen!