Now I find a better solution. NOTE: Table creature_proto_difficulty will be dropped!
I Added a new table 'creature_difficulty' with the following columns:
entry (Base entry to link the difficulty)
difficulty_1 (linked entry from creature_proto table for dungeon: heroic / raid: 25 man)
difficulty_2 (linked entry from creature_proto table for raid: heroic 10 man)
difficulty_3 (linked entry from creature_proto table for raid: heroic 25 man)
The table data are from latest tdb (special thanks to them). So we should have all difficulties now
With the new handling we can define creature_names differences too. NOTE: If you have added custom rows to creature_proto_difficulty you should transfer your data to creature_proto (with an unused new creature_entry) and link the difficulty in table creature_difficulty.
These changes are currently ONLY on the develop branch.