Deal l with temporary contention in pkgdb_transaction_begin() by retrying
    up to NTRIES times. This avoids "database is locked" failures under
    contention.
    Retry up to NTRIES times in get_pragma() when sqlite fails with
    SQLITE_BUSY. This function is called outside of a transaction and so
    isn't handled by the retries in pkgdb_transaction_begin().
Small whitespace cleanup