Implement check that Lefts/ascertainIn/calculateFor do not contain the same population multiple times. #2
Description
Currently, a user can repeat a population name in the comma separated lists provided to Lefts/ascertainIn/calculateFor, which throws RAS calculation off balance, since the repeated individuals are counted multiple times in the Allele count determination etc.
A quick check that no elements of these lists are duplicated should be implemented, and an error thrown. Execution can then continue while only using the unique elements of each list.