provide a way to delete an entities from the database

Hi,
I'm not sure if this is intended by the design of the vcs api, so i'll make my use case clear:
Currently for importing commits from a git repo, we parse the branch list to get a list of all branches. We just use VersioncontrolLabel::ensureLabel to ensure that a label is in the db. We have no idea when a branch was added, who did it or why, so we don't create any VersioncontrolOperation for branch creation, ever. This could change with a update-hook, but i'd still like to support the log parser anyways. This means we currently display a branch just as an attribute of a commit in the commit log. That's fine, but with git you'll add and remove a lot of branches, and we don't want already deleted branches to show up in the commit log. this means, when a branch is deleted in a git repo, we currently just delete the label from the database and remove it from all commits which are in a given branch (potentially many!).
The way this is done is extremly hacky, and it should at least get in the API. Maybe we should also think of a way of optimizing the deletion of branches, maybe through a boolean column deleted in the labels table, and modifying every query for versioncontrol_labels to not include labels with a status of deleted = 1. The cleanup of the table (remove deleted branches from the VCOperations and from the labels table) then could go into cron or could just get a seperate button, so it doesn't block the whole vcs_api.

The code i currently use for that is the following:

/**
 * This function removes the given branch from all commits.
 * @param VersioncontrolRepository $repository
 * @param string $branch
 * @return none
 */
function _versioncontrol_git_log_remove_branch_from_commits($repository, $branch) {
  $constraints = array(
    'vcs' => array('git'),
    'repo_ids' => array($repository->repo_id),
    'types' => array(VERSIONCONTROL_OPERATION_COMMIT),
    'branches' => array($branch),
  );
  $commits_as_op = VersioncontrolOperationCache::getInstance()->getOperations($constraints);
  foreach($commits_as_op as $commit_op) {
    $new_labels = array();
    foreach($commit_op->labels as $label) {
      if($label->type == VERSIONCONTROL_LABEL_BRANCH && $label->name != $branch) {
        $new_labels[] = $label;
      }
    }
    $commit_op->updateLabels($new_labels);
  }
}



  // Deleted branches are removed, commits in them are not!
  // TODO: the db_query in here is not nice, that should be part of vcapi!
  foreach($branches_deleted as $branch_name) {
    _versioncontrol_git_log_remove_branch_from_commits($repository, $branch_name);
    db_query('DELETE FROM {versioncontrol_labels}
              WHERE repo_id = %d AND type = %d AND label_id = %d',
              $repository->repo_id, VERSIONCONTROL_LABEL_BRANCH,
              $branch_label_list[$branch_name]->label_id);
  }