input alignment filename varies between `bytes` and `str` in two places

[byb121]

As the two commented lines indicate:

parabam/parabam/core.pyx

Line 674 in 77610b3

print "I feel there's a line somewhere in the code, if we correct it we don't need to do this. Why input path is not bytes again?"

parabam/parabam/chaser.pyx

Line 90 in 77610b3

print "how come parent_bam_file_name is not in bytes again."

This is likely caused by an unstable object type of filename attribute of pysam.AlignmentFile, but requires a closer check.