Avoid duplicate VEP information for databases with chromosome differences like hg19/GRCh37.

def _special_dbkey_maps(dbkey, ref_file):
    """Avoid duplicate VEP information for databases with chromosome differences like hg19/GRCh37.
    """
    remaps = {"hg19": "GRCh37",
              "hg38-noalt": "hg38"}
    if dbkey in remaps:
        base_dir = os.path.normpath(os.path.join(os.path.dirname(ref_file), os.pardir))
        vep_dir = os.path.normpath(os.path.join(base_dir, "vep"))
        other_dir = os.path.relpath(os.path.normpath(os.path.join(base_dir, os.pardir, remaps[dbkey], "vep")),
                                    base_dir)
        if os.path.exists(os.path.join(base_dir, other_dir)):
            if not os.path.lexists(vep_dir):
                os.symlink(other_dir, vep_dir)
            return vep_dir
        else:
            return None
    else:
        return None