incorrect error message for useunion attribute

Submitted by Kristof Szabados

Link to original bug (#537168)

Description

For this code:

type record E22_correct { 
         enumerated {alt_, alt_1, alt_2} xsiType optional,
         enumerated {x20, x50_0, small_1} content
       }
       with {
             variant "name as uncapitalized";
             variant "element";
             variant "useUnion";
}

the compiler reports "USE-UNION can only be applied to a CHOICE/union type"

But according to B.3.16 of "Part 9: Using XML schema with TTCN-3" it is allowed to apply the useUnion attribute to record types.

Version: 6.4.0