delete_orphaned_terms 6.x-2.x-dev

#726654: by jmroth: adding many new features
Excerpt from README.txt:

FEATURES
--------
- manual pruning of specific (or simply all) vocabularies
- automatic pruning with whitelist/blacklist (see below)
- failsafe parameter for automatic mode including message to error log
- simulation of what would be removed (manually or by the automatic job)
- option to only prune tag based vocabularies (this is usually where the biggest mess is)
- option to remove empty vocabularies (dependent on whitelist/blacklist)
- configurable setting of what "orphaned" means
More goodies:
- works with i18n (prunes all languages)
- logs to watchdog() if something gets removed (info) or failsafe is triggered (error)
- code review is happy, even at the strictest setting