Validation: allow multi-sample reference files
Validation: allow multi-sample reference files

https://groups.google.com/d/msgid/biovalidation/d9b975b0-9fd7-4bd6-b96a-988f64e65e36%40googlegroups.com

chapmanb/bcbio-nextgen,a113n/bcbio-nextgen,chapmanb/bcbio-nextgen,biocyberman/bcbio-nextgen,vladsaveliev/bcbio-nextgen,a113n/bcbio-nextgen,biocyberman/bcbio-nextgen,lbeltrame/bcbio-nextgen,vladsaveliev/bcbio-nextgen,vladsaveliev/bcbio-nextgen,lbeltrame/bcbio-nextgen,chapmanb/bcbio-nextgen,a113n/bcbio-nextgen,lbeltrame/bcbio-nextgen,biocyberman/bcbio-nextgen