subject.list: List to describe the file of subject ids
Description
The list to describe the file of subject ids for snp.listDetails
This list is should only be used when the genotype file does not contain subject ids.
The order of the ids in this file must match the order of the genotypes in the genotype file.
If the genotype data is in a PLINK format, then id.var
must be of length 2 corresponding the the family id and subject id.
When using the GxE.scan function, this list can often just be set to the name of the file
containing the ids.