Add function for removing perms from a role

I suggest adding this to user include. I also suggest renaming install_set_permissions() to install_add_permissions() since thats all it can do due to $perms = array_unique(array_merge($perms, (array)$existing_perms));. That code is useful for set and forget adding of a perm so thats why I propose to keep the function, but change its name.

/**
 * Remove permissions for a certain role.
 */
function install_remove_permissions($rid, $perms) {
  // Retrieve the currently set permissions.
  $result = db_query("SELECT p.perm FROM {role} r INNER JOIN {permission} p ON p.rid = r.rid WHERE r.rid = %d ", $rid);
  $existing_perms = array();
  while ($row = db_fetch_object($result)) {
    $existing_perms += explode(', ', $row->perm);
  }
  $new_perms = array_diff($existing_perms, $perms);
  
  // Update the permissions.
  db_query('DELETE FROM {permission} WHERE rid = %d', $rid);
  db_query("INSERT INTO {permission} (rid, perm) VALUES (%d, '%s')", $rid, implode(', ', $new_perms));
}