Separate log of wrong and empty responses

Good idea,

And maybe, we can take this a bit further:
- provide a hook "hook_captcha_log($form_id, $solution, $response, ...)" that would be called on CAPTCHA issues: wrong response, empty response, CAPTCHA session reuse attack, ...
- move the handling of these log items to a separate module, to make the core CAPTCHA module a bit lighter (both in UI and in code) and still allow for more advanced processing of the issues in the external/optional module (e.g. daily summary, weekly summary, email warnings, ...)

What do you think?

PS: if you create patches, it is indeed recommended to do it against 6.x-2.x-dev (CVS branch DRUPAL-6--2), there seem to be a problem with the automated test system. Anyway, even though you created the patch against 6.x-2.3, it could still be applicable to CVS branch DRUPAL-6--2. Let's try...

#1002246: variable_set('captcha_wrong_response_counter',...) is expensive performance wise (clears cache) might also be relevant to take into account here

if (variable_get('captcha_log_wrong_responses', FALSE)) {
  $wrongCount = db_result(db_query("select count(*) as cnt from {watchdog} where type = 'CAPTCHA'   AND severity = " . WATCHDOG_INFO));
}
$form['captcha_log_failures']['captcha_log_wrong_responses'] = array(
     '#type' => 'checkbox',
     '#title' => t('Log wrong responses'),
    '#description' => t('Report information about wrong responses to the !log.', array('!log' => l(t('log'), 'admin/reports/dblog'))),
    '#description' => t('Probably valid user. Currently: !wrongCount',  array('!wrongCount' => $wrongCount)),
     '#default_value' => variable_get('captcha_log_wrong_responses', FALSE),
);

The problem is that when the variable "captcha_log_wrong_responses" is false, you use the $wrongCount variable (in the description) without it being defined/assigned a value.

Also some minor remarks about code style:
- In Drupal code, we use two spaces for indentation
- we put the opening brace "{" on the same line as the "for", "function", "if"
- we don't use camel case/dromedaris case ($wrongCount), but underscores: $wrong_count
more info here: http://drupal.org/coding-standards

thanks for your work