eliminate seek()s

Fixes https://github.com/ged-lab/khmer/issues/633
On Tue, Nov 04, 2014 at 11:15:58AM -0800, Michael R. Crusoe wrote:
> >      compression = None
> >      for magic, ftype in magic_dict.items():
> >          if file_start.startswith(magic):
> >              compression = ftype
> >              break
> > -    sequencefile = {
> > -        'gz': lambda: gzip.open(filename),
> > -        'bz2': lambda: bz2.BZ2File(filename),
> > -        'zip': lambda: zipfile.ZipFile(filename),
> > -        None: lambda: _open(filename)}[compression]()
> > -
> > -    line = sequencefile.readline()
> > -
> > -    if not line:
> > -        return []
> 
> The current screed returns an empty list in the instance of an empty file. @ctb shall I retain this behaviour or throw an exception? (Like we do for an unknown file format)

+0 for returning empty list.  I don't have a strong reason for this but
there is nothing technically wrong with an empty file, is there? :)

cheers,
--titus
-- 
C. Titus Brown, ctb@msu.edu