Checks if a record is valid for processing.

def record_is_valid(record):
    "Checks if a record is valid for processing."

    # No random contigs
    if record.CHROM.startswith('GL'):
        return False

    # Skip results with a read depth < 5. If no read depth is specified then
    # we have no choice but to consider this record as being valid.
    if 'DP' in record.INFO and record.INFO['DP'] < 5:
        return False

    return True