Fixed issue #8160: queXML export: ambigous variable names in text/number/dual matrix question

Dev: Variable names are now built as:
Dev: [questioncode]_[y-scale code]_[x-scale code].
Dev: Varnames are thus compatible with VV-export,
Dev: Stata-XML and so on and so forth, which facilitates
Dev: easy merging of data collected with quexf and LS