issue 54: fixed missing assignment to pytype in tags.__set__
issue 54: fixed missing assignment to pytype in tags.__set__

--HG--
branch : dev-0.4

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