escape column names in ORDER BY clause
physically deleting zombies: no privs required
allow to set $inactive directly from $rv['problems']
dont disable DANGLING-option automatically; always show checkbox
new api for sql_delete_*()
- handle actions 'dryrun', 'soft', 'hard'
- always return a-array with fields 'problems', 'deletable', 'deleted'
use that in sql_delete_{logbook,changelog,sessions} and corresponding sql_prune_*() functions
remove dead code
allow db row as $item
deleting:
  - sql_delete_generic(): a generic delete handler checking privs and references
  - re-order functions in code/mysql.php
changelog:
  - rename columns: 'table' => 'tname', 'key' => 'tkey' (to avoid sql keywords)
  - delete changlog entries when physically deleting corresponding entry
use sql_delete_generic() where possible; use new deletion-api in all sql_delete-*() functions