Update calignmentfile.pyx
Update calignmentfile.pyx

Error message ("file has no sequences defined") was misleading.  The argument is check_sq, not check_seq.  Also, the message should suggest setting it to False, since True is the default.
TyberiusPrime/pysam,kyleabeauchamp/pysam,kyleabeauchamp/pysam,bioinformed/pysam,bioinformed/pysam,TyberiusPrime/pysam,pysam-developers/pysam,TyberiusPrime/pysam,TyberiusPrime/pysam,pysam-developers/pysam,kyleabeauchamp/pysam,pysam-developers/pysam,bioinformed/pysam,kyleabeauchamp/pysam,pysam-developers/pysam,kyleabeauchamp/pysam,bioinformed/pysam,bioinformed/pysam,TyberiusPrime/pysam