Add a note about tile enum ordering (gammafunk, SamB)
Use some constants as they were intended (SamB).
Comment tile enums that need to be removed on major bump.
We don't want to remove the returning tile on bump, just move it down
Generalise some flight checks, fix inconsistencies

Flight from innate ability, potion, evokable item or spell is now
consistently prevented by tree form, liquefaction and grasping roots.

Most cases also correctly abort without costing a turn, potions are still
wasted at the moment though.
Add a Pan lord to pan_disco_hall
Fix a crash on melding the macabre finger necklace.

Also, fix the assert being not picky enough.
More "must be in same order" warnings in dc-item.txt
"save compatibility is broken" -> "TAG_MAJOR_VERSION > 34"
We still have missiles of confusion, too ...

(Also tweak the comment for returning a bit.)