Fix #2107 - flatten resource references arrays properly

Resource parameters of the form
[Res[a], Res[a,b]] ends being evaluated as
[Res[a], [ Res[a], Res[b] ]
This last form was not flattened when transfomed into RAL
type, which in turn prevented the sub array to be converted
in regular resource references.
Thus the type was choking when encountering those native
parser references instead of usual resource reference.
The fix consists in flattening array of references before
transformation to trans objects for RAL.

Signed-off-by: Brice Figureau <brice-puppet@daysofwonder.com>