XO returns wrong collection size for multiple collections annotated with the same relation

[obfischer]

Given the following code fragment:

@Relation("HAS_ITEM")
List<YMLSequenceDescriptor> getSequences();

@Relation("HAS_ITEM")
List<YMLMapDescriptor> getMaps();

@Relation("HAS_ITEM")
List<YMLScalarDescriptor> getScalars();

And assuming that any of the three collections contains three elements, then calling .size() on every collection returns 3.

IMHO the correct behaviour would be, that only the collection for sequences should return 3, while all other shoudl return only zero.

[DirkMahler]

Duplicates #172

I'd like to treat this more as a feature than a bug: The model in the datastore is ambiguous, XO shall be able to compensate for that.