To do this I have added a RodBindingCollection which can represent either a VCF or a
file of VCFs. Note that e.g. SelectVariants allows a list of RodBindingCollections so
that one can intermix VCFs and VCF lists.
For VariantContext tags with a list, by default the tags for the -V argument are applied
unless overridden by the individual line. In other words, any given line can have either
one token (the file path) or two tokens (the new tags and the file path). For example:
foo.vcf
VCF,name=bar bar.vcf
Note that a VCF list file name must end with '.list'.
Added this functionality to CombineVariants, CombineReferenceCalculationVariants, and VariantRecalibrator.
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