PR# 19982 Conversion querieswith the same feature name

When we have two conversion queries of the form:

```eiffel
convert
    f: {CC},
    f: {DD}
```

EiffelStudio reports a VNCP validity error complaining that routine `f` is specified twice in the convert clause. But there is nothing in the Eiffel standard which forbids this. It should be equivalent to:

```eiffel
convert
    f: {CC, DD}
```

--
Eric Bezault

class BB

convert

	f: {CC},
	f: {DD}

feature

	f: CC
		do
			create Result
		end

end
~~~~
class CC

inherit

	DD

end
~~~~
class DD

end