{AH} fix py2 issue: IOError instead of OSError
{AH} fix py2 issue: IOError instead of OSError

pysam-developers/pysam,pysam-developers/pysam,pysam-developers/pysam,kyleabeauchamp/pysam,pysam-developers/pysam,kyleabeauchamp/pysam,kyleabeauchamp/pysam,kyleabeauchamp/pysam,kyleabeauchamp/pysam