'Determines whether the file is a velveth produced  fasta format
The id line has 3 fields separated by tabs: sequence_name  sequence_index category::
>SEQUENCE_0_length_35   1       1
GGATATAGGGCCAACCCAACTCAACGGCCTGTCTT
>SEQUENCE_1_length_35   2       1
CGACGAATGACAGGTCACGAATTTGGCGGGGATTA'

def sniff(self, filename):

    try:
        fh = open(filename)
        while True:
            line = fh.readline()
            if (not line):
                break
            line = line.strip()
            if line:
                if line.startswith('>'):
                    if (not re.match('>[^\\t]+\\t\\d+\\t\\d+$', line)):
                        break
                    line = fh.readline().strip()
                    if ((line == '') or line.startswith('>')):
                        break
                    return True
                else:
                    break
        fh.close()
    except:
        pass
    return False
