intg: Do not use non-existent pre-increment
    
    Do not try to use the pre-increment operator which doesn't exist in
    Python (and is in fact two "identity" operators - opposites of
    "negation" operators). Use addition and assignment instead.
    
    This fixes infinite loops on failed slapd starting and stopping.
    
    Reviewed-by: Michal Židek <mzidek@redhat.com>