Improve error message on function argument type mismatch

Currently, when a function argument is of the wrong type, the reply is an error message like this:

```
GRAPH.QUERY g "RETURN subString('abcde', 2, 'z')"
(error) Type mismatch: expected Integer but was String
```

It would be more helpful if the reply was an error message like this:

```
(error) Type mismatch on function 'subString' argument 3: expected Integer but was String
```
