Tighten phylip sniffer

            if any(str.isdigit(c) for c in seq):

                # Could tighten up further by requiring IUPAC strings chars

                return False

        line = alignment_prefix.readline()

        if line.strip():

            # There should be a newline separating alignments.

            # If we got more content this is probably not a phylip file

            return False

        # There may be more lines with the remaining parts of the sequences

        return True

        >>> fname = get_test_fname('test_relaxed_interleaved.phylip')

        >>> Phylip().sniff(fname)

        True

        >>> fname = get_test_fname("not_a_phylip_file.tabular")

        >>> Phylip().sniff(fname)

        False

        """

        f = file_prefix.string_io()

        # Get number of sequences and sequence length from first line

1	2

A	B

D	E

X	Y

1	2