xsd2ttcn: name clash with different capitalization

Reported on the forum: https://www.eclipse.org/forums/index.php?t=rview&goto=1869030#msg_1869030

If a definition in the XSD has the same name, but with different capitalization, as a definition in an imported XSD, then these might clash in the generated TTCN-3 module, since their capitalization can change.

In the example from the forum the type 'entryType' (from an imported XSD) is used as the type of an element, and there is also a type called 'EntryType' defined in that XSD. In TTCN-3 both of these are converted into types called 'EntryType' (with different variant attributes). The mentioned element's type is simply converted into 'EntryType', with the converter assuming, that a module prefix is not needed, since it doesn't think the types generated from 'entryType' and 'EntryType' might clash.

/cc @aknappqwt @mmagyari