added warning for duplicate @RG tag in header
added warning for duplicate @RG tag in header

iontorrent/bamtools,pezmaster31/bamtools,sksaskrobinsons/code,pezmaster31/bamtools,domibel/bamtools,kdmurray91/bamtools,kdmurray91/bamtools,SANBI-SA/bamtools,iontorrent/bamtools,sksaskrobinsons/code,domibel/bamtools,boratonAJ/bamtools,pezmaster31/bamtools,pezmaster31/bamtools,boratonAJ/bamtools,SANBI-SA/bamtools