issue 91: fixed quadratic behaviour in header generation for sam files
issue 91: fixed quadratic behaviour in header generation for sam files

carolinux/pysam,pysam-developers/pysam,brendanofallon/pysam,mattions/pysam,carolinux/pysam,nlhepler/pysam,brendanofallon/pysam,kyleabeauchamp/pysam,TyberiusPrime/pysam,bioinformed/pysam,TyberiusPrime/pysam,dannon/pysam,brendanofallon/pysam,mattions/pysam,dannon/pysam,brendanofallon/pysam,TyberiusPrime/pysam,pysam-developers/pysam,kyleabeauchamp/pysam,carolinux/pysam,pysam-developers/pysam,daler/pysam,nlhepler/pysam,nlhepler/pysam,kyleabeauchamp/pysam,daler/pysam,daler/pysam,TyberiusPrime/pysam,bioinformed/pysam,mattions/pysam,bioinformed/pysam,nlhepler/pysam,kyleabeauchamp/pysam,carolinux/pysam,nlhepler/pysam,kyleabeauchamp/pysam,mattions/pysam,daler/pysam,carolinux/pysam,daler/pysam,dannon/pysam,mattions/pysam,dannon/pysam,bioinformed/pysam,TyberiusPrime/pysam,dannon/pysam,pysam-developers/pysam,bioinformed/pysam,brendanofallon/pysam